Thermal ion effects on kinetic beta-induced Alfven eigenmodes excited by energetic ions
Energy Technology Data Exchange (ETDEWEB)
Qi Longyu; Sheng, Z. M. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Dong, J. Q. [Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou 310027 (China); Southwestern Institute of Physics, Chengdu 610041 (China); Bierwage, A. [Aomori Research and Development Center, Japan Atomic Energy Agency, Rokkasho, Aomori 039-3212 (Japan); Lu Gaimin [Southwestern Institute of Physics, Chengdu 610041 (China)
2013-03-15
Kinetic beta-induced Alfven eigenmodes (KBAEs) driven by energetic ions are numerically investigated using revised AWECS code. The thermal ion density and temperature gradients are taken into account. It is found that the growth rate of the KBAEs increases with the thermal ion pressure gradient, and the contributions from the density gradient and temperature gradient of the thermal ions to the enhancement of the instability are comparable. The damping effect of thermal ion dynamics on the modes is also observed.
Nonlinear dynamics of beta induced Alfv\\'en eigenmode driven by energetic particles
Wang, X; Chen, L; Fogaccia, G; Di Troia, C; Vlad, G; Zonca, F
2012-01-01
Nonlinear saturation of beta induced Alfv\\'en eigenmode, driven by slowing down energetic particles via transit resonance, is investigated by the nonlinear hybrid magnetohyrodynamic gyro-kinetic code (XHMGC). Saturation is characterized by frequency chirping and symmetry breaking between co- and counter-passing particles, which can be understood as the the evidence of resonance-detuning. The scaling of the saturation amplitude with the growth rate is also demonstrated to be consistent with radial resonance detuning due to the radial non-uniformity and mode structure.
Fine Structure Zonal Flow Excitation by Beta-induced Alfven Eigenmode
Qiu, Zhiyong; Zonca, Fulvio
2016-01-01
Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced Alfven eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It is found that electrostatic zonal flow (ZF), rather than zonal current, is preferentially excited by finite amplitude BAE. In addition to the well-known meso-scale radial envelope structure, ZF is also found to exhibit fine radial structure due to the localization of BAE with respect to mode rational surfaces. Specifically, the zonal electric field has an even mode structure at the rational surface where radial envelope peaks.
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N.N. [Princeton Plasma Physics Laboratory, Princeton University (United States)], E-mail: ngorelen@pppl.gov; Berk, H.L. [IFS, Austin, Texas (United States); Fredrickson, E. [Princeton Plasma Physics Laboratory, Princeton University (United States); Sharapov, S.E. [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire (United States)
2007-10-08
New global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfven-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high-beta >20%. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfven coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.
Magneto-HydroDynamic activity and Energetic Particles - Application to Beta Alfven Eigenmodes
Nguyen, Christine
2009-01-01
The goal of magnetic fusion research is to extract the power released by fusion reactions and carried by the product of these reactions, liberated at energies of the order of a few MeV. The feasibility of fusion energy production relies on our ability to confine these energetic particles, while keeping the thermonuclear plasma in safe operating conditions. For that purpose, it is necessary to understand and find ways to control the interaction between energetic particles and the thermonuclear plasma. Reaching these two goals is the general motivation for the work conducted during the PhD. More specifically, our focus is on one type of instability, the Beta Alfven Eigenmode (BAE), which can be driven by energetic particles and impact on the confinement of both energetic and thermal particles. In this work, we study the characteristics of BAEs analytically and derive its dispersion relation and structure. Next, we analyze the linear stability of the mode in the presence of energetic particles. First, a purely l...
Magneto-Hydrodynamic Activity and Energetic Particles - Application to Beta Alfven Eigenmodes
International Nuclear Information System (INIS)
The goal of magnetic fusion research is to extract the power released by fusion reactions and carried by the product of these reactions, liberated at energies of the order of a few MeV. The feasibility of fusion energy production relies on our ability to confine these energetic particles, while keeping the thermonuclear plasma in safe operating conditions. For that purpose, it is necessary to understand and find ways to control the interaction between energetic particles and the thermonuclear plasma. Reaching these two goals is the general motivation for this work. More specifically, our focus is on one type of instability, the Beta Alfven Eigenmode (BAE), which can be driven by energetic particles and impact on the confinement of both energetic and thermal particles. In this work, we study the characteristics of BAEs analytically and derive its dispersion relation and structure. Next, we analyze the linear stability of the mode in the presence of energetic particles. First, a purely linear description is used, which makes possible to get an analytical linear criterion for BAE destabilization in the presence of energetic particles. This criterion is compared with experiments conducted in the Tore-Supra tokamak. Secondly, because the linear analysis reveals some features of the BAE stability which are subject to a strong nonlinear modification, the question is raised of the possibility of a sub-critical activity of the mode. We propose a simple scenario which makes possible the existence of meta-stable modes, verified analytically and numerically. Such a scenario is found to be relevant to the physics and scales characterizing BAEs. (author)
Beta-induced Alfven-acousti Eigenmodes in NSTX and DIII-D Driven by Beam Ions
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N. N.; Van Zeeland, M. A.; Berk, H. L.; Crocker, N. A.; Darrow, D.; Fredrickson, E.; Fu, G. Y.; Heidbrink, W. W.; Menard, J.; Nazikian, R.
2009-03-06
Kinetic theory and experimental observations of a special class of energetic particle driven instabilities called here Beta-induced Alfven-Acoustic Eigenmodes (BAAE) are reported confirming previous results [N.N. Gorelenkov H.L. Berk, N.A. Crocker et. al. Plasma Phys. Control. Fusion 49 B371 (2007)] The kinetic theory is based on the ballooning dispersion relation where the drift frequency effects are retained. BAAE gaps are recovered in kinetic theory. It is shown that the observed certain low-frequency instabilities on DIII-D [J.L. Luxon, Nucl. Fusion 42 614 (2002)] and National Spherical Torus Experiment [M. Ono, S.M. Kaye, Y.-K M. Peng et. al., Nucl. Fusion 40 3Y 557 (2000)] are consistent with their identification as BAAEs. BAAEs deteriorated the fast ion confinement in DIII-D and can have a similar effect in next-step fusion plasmas, especially if excited together with multiple global Toroidicity-induced shear Alfven Eigenmode (TAE) instabilities. BAAEs can also be used to diagnose safety factor profiles, a technique known as magnetohydrodynamic spectroscopy.
Phenomenology of Compressional Alfven Eigenmodes
International Nuclear Information System (INIS)
Coherent oscillations with frequency 0.3 (le) ω/ωci (le) 1, are seen in the National Spherical Torus Experiment [M. Ono, S.M. Kaye, Y-K.M. Peng, (and others), Nucl. Fusion 40, 557 (2000)]. This paper presents new data and analysis comparing characteristics of the observed modes to the model of compressional Alfven eigenmodes (CAE). The toroidal mode number has been measured and is typically between 7 < n < 9. The polarization of the modes, measured using an array of four Mirnov coils, is found to be compressional. The frequency scaling of the modes agrees with the predictions of a numerical 2-D code, but the detailed structure of the spectrum is not captured with the simple model. The fast ion distribution function, as calculated with the beam deposition code in TRANSP [R.V. Budny, Nucl. Fusion 34, 1247 (1994)], is shown to be qualitatively consistent with the constraints of the Doppler-shifted cyclotron resonance drive model. This model also predicts the observed scaling of the low frequency limit for CAE
Kinetic Damping of Toroidal Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
G.Y. Fu; H.L. Berk; A. Pletzer
2005-05-03
The damping of Toroidal Alfven Eigenmodes in JET plasmas is investigated by using a reduced kinetic model. Typically no significant damping is found to occur near the center of the plasma due to mode conversion to kinetic Alfven waves. In contrast, continuum damping from resonance near the plasma edge may be significant, and when it is, it gives rise to damping rates that are compatible with the experimental observations.
Characteristics of Short Wavelength Compressional Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
Fredrickson, E D; Podesta, M; Bortolon, A; Crocker, N A; Gerhardt, S P; Bell, R E; Diallo, A; LeBlanc, B; Levinton, F M
2012-12-19
Most Alfvenic activity in the frequency range between Toroidal Alfven Eigenmodes and roughly one half of the ion cyclotron frequency on NSTX [M. Ono, et al., Nucl. Fusion 40 (2000) 557], that is, approximately 0.3 MHz up to ≈ 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n=1 kink-like mode. In this paper we present measurements of the spectrum of these high frequency CAE (hfCAE), and their mode structure. We compare those measurements to a simple model of CAE and present evidence of a curious non-linear coupling of the hfCAE and the low frequency kink-like mode.
Continuum damping of ideal toroidal Alfven eigenmodes
International Nuclear Information System (INIS)
A perturbation theory based on the two dimensional (2D) ballooning transform is systematically developed for ideal toroidal Alfven eigenmodes (TAEs). A formula, similar to the Fermi golden rule for decaying systems in quantum mechanics, is derived for the continuum damping rate of the TAE; the decay (damping) rate is expressed explicitly in terms of the coupling of the TAE to the continuum spectrum. Numerical results are compared with previous calculations. It is found that in some narrow intervals of the parameter mε the damping rate varies very rapidly. These regions correspond precisely to the root missing intervals of the numerical solution by Rosenbluth et al
Alfven eigenmodes in shear reversed plasmas
International Nuclear Information System (INIS)
Experiments on JT-60U and JET have shown that plasma configurations with shear reversal are prone to the excitation of unusual Alfven Eigenmodes by energetic particles. These modes emerge outside the TAE frequency gap, where one might expect them to be strongly damped. The modes often appear in bunches and they exhibit a quasi-periodic pattern of predominantly upward frequency sweeping (Alfven Cascades) as the safety factor q changes in time. This work presents a theory that explains the key features of the observed unusual modes including their connection to TAE's as well as the modifications of TAE's themselves near the shear reversal point. The developed theory has been incorporated into a reduced numerical model and verified with full geometry codes. JET experimental data on Alfven spectroscopy have been simulated to infer the mode numbers and the evolution of qmin in the discharge. This analysis confirms the values of q that characterize the internal transport barrier triggering in reversed shear plasmas. (author)
Discrete compressional Alfven eigenmode spectrum in tokamaks
International Nuclear Information System (INIS)
The spectrum of Compressional Alfven Eigenmodes (CAE) is analyzed and shown to be discrete in tokamaks with low aspect ratio, such as the National Spherical Torus Experiment (NSTX), as well as in the conventional tokamaks, such as DIII-D. The study is focused on recent similarity experiments on NSTX and DIII-D in which sub-cyclotron frequency instabilities of CAEs were observed at similar plasma conditions [W.W. Heidbrink, et.al. Nuclear Fusion 46, 2006, in press]. The global ideal MHD code NOVA recovers the main properties of these modes predicted by theory and observed in both devices. The discrete spectrum of CAEs is characterized by three quantum mode numbers for each eigenmode, (M;S;n), where M, S, and n are poloidal, radial and toroidal mode numbers, respectively. The expected mode frequency splitting corresponding to each of these mode numbers seems to be observed in experiments and is consistent with our numerical analysis. The polarization of the observed magnetic field oscillations in NSTX was measured and is also consistent with the numerical analysis, which helps to identify them as CAE activity. CAE mode structure was obtained and shown to be localized in both radial and poloidal directions with typical radial localization toward the plasma edge and poloidal localization at the low field side of the plasma cross section. (author)
Discrete compressional Alfven eigenmode spectrum in tokamaks
International Nuclear Information System (INIS)
The spectrum of compressional Alfven eigenmodes (CAE) is analysed and shown to be discrete in tokamaks with low aspect ratio, such as the National Spherical Torus Experiment (NSTX), as well as in conventional tokamaks, such as DIII-D. The study is focused on recent similarity experiments on NSTX and DIII-D in which sub-cyclotron frequency instabilities of CAEs were observed at similar plasma conditions (W.W. Heidbrink et al 2006 Nucl. Fusion 46 324). The global ideal MHD code NOVA recovers the main properties of these modes predicted by theory and observed in both devices. The discrete spectrum of CAEs is characterized by three quantum mode numbers for each eigenmode (M, S and n), where M, S and n are poloidal, radial and toroidal mode numbers, respectively. The expected mode frequency splitting corresponding to each of these mode numbers seems to be observed in experiments and is consistent with our numerical analysis. The polarization of the observed magnetic field oscillations in NSTX was measured and is also consistent with the numerical analysis, which helps to identify them as CAE activity. CAE mode structure was obtained and shown to be localized in both radial and poloidal directions with typical radial localization toward the plasma edge and poloidal localization at the low field side of the plasma cross section
Alfven eigenmodes and their impact on plasma characteristics in JT-60U
International Nuclear Information System (INIS)
In weak or reversed magnetic shear plasmas of JT-60U, the excitation and the stabilization of Alfven eigenmodes and their impact on energetic ion confinement were investigated with the negative-ion-based neutral beam injection at 330-360 keV. Toroidicity-induced Alfven eigenmodes (TAEs) were observed in weak shear plasmas with h>≥0.1% and 0.4≤vbparallel/vA≤1. The stability of TAEs is consistent with the predictions by the NOVA-K code. New burst modes and chirping modes were observed at a higher beta regime of h>≥0.2%. The effect of TAEs, burst modes and chirping modes on the fast ion confinement is small so far. The strongly-reversed shear plasma with the internal transport barrier suppresses Alfven eigenmodes. (author)
MHD-Vlasov simulation of the toroidal Alfven eigenmode
International Nuclear Information System (INIS)
A new simulation method has been developed to investigate the excitation and saturation processes of toroidal Alfven eigenmodes (TAE modes). The background plasma is described by a full-MHD fluid model, while the kinetic evolution of energetic alpha particles is followed by the drift kinetic equation. The magnetic fluctuation of n = 2 mode develops and saturates at the level of 1.8x10-3 of the equilibrium field when the initial beta of alpha particles is 2% at the magnetic axis. After saturation, the TAE mode amplitude shows an oscillatory behavior with a frequency corresponding to the bounce frequency of the alpha particles trapped by the TEA mode. The decrease of the power transfer rate from the alpha particles to the TAE mode, which is due to the trapped particle effect of a finite-amplitude wave, causes the saturation. From the linear growth rate the saturation level can be estimated. (author)
Alpha particle destabilization of the toroidicity-induced Alfven eigenmodes
International Nuclear Information System (INIS)
The high frequency, low mode number toroidicity-induced Alfven eigenmodes (TAE) are shown to be driven unstable by the circulating and/or trapped α-particles through the wave-particle resonances. Satisfying the resonance condition requires that the α-particle birth speed vα ≥ vA/2|m-nq|, where vA is the Alfven speed, m is the poloidal model number, and n is the toroidal mode number. To destabilize the TAE modes, the inverse Landau damping associated with the α-particle pressure gradient free energy must overcome the velocity space Landau damping due to both the α-particles and the core electrons and ions. The growth rate was studied analytically with a perturbative formula derived from the quadratic dispersion relation, and numerically with the aid of the NOVA-K code. Stability criteria in terms of the α-particle beta βα, α-particle pressure gradient parameter (ω*/ωA) (ω* is the α-particle diamagnetic drift frequency), and (vα/vA) parameters will be presented for TFTR, CIT, and ITER tokamaks. The volume averaged α-particle beta threshold for TAE instability also depends sensitively on the core electron and ion temperature. Typically the volume averaged α-particle beta threshold is in the order of 10-4. Typical growth rates of the n=1 TAE mode can be in the order of 10-2ωA, where ωA=vA/qR. Other types of global Alfven waves are stable in D-T tokamaks due to toroidal coupling effects
Nonlinear hybrid simulation of toroidicity-induced alfven eigenmode
International Nuclear Information System (INIS)
Gyrokinetic/Magnetohydrodynamics hybrid simulations have been carried out using MH3D-K code to study the nonlinear saturation of the toroidicity-induced Alfven eigenmode driven by energetic particles in a tokamak plasma. It is shown that the wave particle trapping is the nonlinear saturation mechanism for the parameters considered. The corresponding density profile flattening of hot particles is observed. The saturation amplitude is proportional to the square of linear growth rate. In addition to TAE modes, a new n = 1, m = 0 global Alfven eigenmode is shown to be excited by the energetic particles
International Nuclear Information System (INIS)
A transition of a core localized type toroidal Alfven eigenmode with n 1 toroidal mode number to two n = 1 global Alfven eignemodes was observed in NBI-heated plasmas in the Compact Helical System (CHS) heliotron/torsatron. This transition phenomenon is interpreted based on the temporal evolution of the rotational transform near the plasma center caused by the increased in the beam-driven current. (author)
Excitation of global Alfven Eigenmodes by RF heating in JET
Energy Technology Data Exchange (ETDEWEB)
Kerner, W.; Borba, D.; Gormezano, C.; Huysmans, G.; Porcelli, F.; Start, D. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Fasoli, A. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP); Sharapov, S. [Kurchatov Institute, Moscow (Russian Federation)
1994-07-01
The alpha-particle confinement of future D-T experiments at JET can be severely degraded by Global Alfven Eigenmodes (AE). Scenarios for the excitation of Alfven Eigenmodes in usual (e.g. D-D) plasmas are proposed, which provide a MHD diagnostic and allow the study of the transport of super-Alfvenic ions. Active studies with separate control of TAE amplitude and energetic particle destabilization, measuring the plasma response, give more information than passive studies, in particular concerning the damping mechanisms. The TAE excitation can be achieved by means of the saddle coil and the ICRH antenna. The experimental method is introduced together with a theoretical model for RF excitation. (authors). 6 refs., 3 figs.
Excitation of global Alfven Eigenmodes by RF heating in JET
International Nuclear Information System (INIS)
The alpha-particle confinement of future D-T experiments at JET can be severely degraded by Global Alfven Eigenmodes (AE). Scenarios for the excitation of Alfven Eigenmodes in usual (e.g. D-D) plasmas are proposed, which provide a MHD diagnostic and allow the study of the transport of super-Alfvenic ions. Active studies with separate control of TAE amplitude and energetic particle destabilization, measuring the plasma response, give more information than passive studies, in particular concerning the damping mechanisms. The TAE excitation can be achieved by means of the saddle coil and the ICRH antenna. The experimental method is introduced together with a theoretical model for RF excitation. (authors). 6 refs., 3 figs
Alfven Eigenmode Stability with Beams in ITER-like Plasma
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov; H.L. Berk; R.V. Budny
2004-07-16
Toroidicity Alfven Eigenmodes (TAE) in ITER can be driven unstable by two groups of energetic particles, the 3.5 MeV {alpha}-particle fusion products and the tangentially injected 1MeV beam ions. Stability conditions are established using the perturbative NOVA/NOVA-K codes. A quasi-linear diffusion model is then used to assess the induced redistribution of energetic particles.
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
International Nuclear Information System (INIS)
A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
Combined Ideal and Kinetic Effects on Reversed Shear Alfven Eigenmodes
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov, G.J. Kramer, and R. Nazikian
2011-05-23
A theory of Reversed Shear Alfven Eigenmodes (RSAEs) is developed for reversed magnetic field shear plasmas when the safety factor minimum, qmin, is at or above a rational value. The modes we study are known sometimes as either the bottom of the frequency sweep or the down sweeping RSAEs. We show that the ideal MHD theory is not compatible with the eigenmode solution in the reversed shear plasma with qmin above integer values. Corrected by special analytic FLR condition MHD dispersion of these modes nevertheless can be developed. Large radial scale part of the analytic RSAE solution can be obtained from ideal MHD and expressed in terms of the Legendre functions. The kinetic equation with FLR effects for the eigenmode is solved numerically and agrees with the analytic solutions. Properties of RSAEs and their potential implications for plasma diagnostics are discussed.
Non-linear modulation of short wavelength compressional Alfven eigenmodes
Energy Technology Data Exchange (ETDEWEB)
Fredrickson, E. D.; Gorelenkov, N. N.; Podesta, M.; Gerhardt, S. P.; Bell, R. E.; Diallo, A.; LeBlanc, B. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Bortolon, A. [University of California, Irvine, California 92697 (United States); Crocker, N. A. [University of California, Los Angeles, California 90095 (United States); Levinton, F. M.; Yuh, H. [Nova Photonics, Princeton, New Jersey 08543 (United States)
2013-04-15
Most Alfvenic activity in the frequency range between toroidal Alfven eigenmodes and roughly one half of the ion cyclotron frequency on National Spherical Torus eXperiment [Ono et al., Nucl. Fusion 40, 557 (2000)], that is, approximately 0.3 MHz up to Almost-Equal-To 1.2 MHz, are modes propagating counter to the neutral beam ions. These have been modeled as Compressional and Global Alfven Eigenmodes (CAE and GAE) and are excited through a Doppler-shifted cyclotron resonance with the beam ions. There is also a class of co-propagating modes at higher frequency than the counter-propagating CAE and GAE. These modes have been identified as CAE, and are seen mostly in the company of a low frequency, n = 1 kink-like mode. In this paper, we present measurements of the spectrum of these high frequency CAE (hfCAE) and their mode structure. We compare those measurements to a simple model of CAE and present a predator-prey type model of the curious non-linear coupling of the hfCAE and the low frequency kink-like mode.
Fokker-Planck-MHD simulation study of Alfven eigenmodes
International Nuclear Information System (INIS)
Nonlinear evolution of fast ions and Alfven eigenmodes, especially the toroidicity-induced Alfven eigenmodes (TAEs), is investigated with two types of Fokker-Planck-MHD simulations. In the first type of simulation, the fast-ion evolution is described by a 4-dimensional Fokker-Planck equation which takes fast-ion source and slowing down into account. The background plasma is described by the nonlinear full MHD equations. A bursting behavior of multiple TAEs, which takes place in neutral beam injection experiments, is reproduced when the slowing-down time is much longer than the mode damping time and the fast-ion pressure is sufficiently high. In the second type of simulation, 5-dimensional Fokker-Planck equation is solved with a linear TAE. In addition to the particle source and slowing down, the pitch-angle scattering is taken into account. The simulation code is benchmarked with the linear behavior of the alpha-particle-driven n=4 TAE in the TFTR D-T plasma. With a realistic pitch-angle-scattering rate and a chosen damping rate, the relaxation time to a steady saturation state is found to be too long to explain the experiment. (author)
Nonlinear MHD Effects on the Alfven Eigenmode Evolution
International Nuclear Information System (INIS)
Two types of hybrid simulations of MHD fluid and energetic particles were carried out to investigate MHD nonlinear effects on Alfven eigenmode evolution. The first type contains fully nonlinear effects of both the MHD fluid and the energetic particles. The second type of the simulation is similar to the first type but different in that the MHD equations are linearized. Comparison between the results of the two types of simulations clarifies the MHD nonlinear effects. A tokamak plasma, where a toroidal Alfven eigenmode (TAE) with toroidal mode number n=4 is the most unstable, was investigated. When the saturation level is δB/B ∼ 2 x 10-2 in the linear MHD simulation results, we found that the saturation and level is δB/B ∼ 8 x 10-8 in the nonlinear MHD simulation results. The MHD nonlinear effects suppress the saturation level of the TAE. Detailed analyses indicate that the suppression effect arises from the change in n=0 harmonics of the magnetic field that is generated by the nonlinear electric field -vTAE x dBTAE, a product of the velocity field and the magnetic field of the TAE. Axisymmetric velocity fields are also generated in the nonlinear run, although the change in the n=0 magnetic field plays the dominant role in the suppression of TAE. (author)
Calculation of continuum damping of Alfv\\'en eigenmodes in 2D and 3D cases
Bowden, G. W.; Hole, M. J.; Könies, A.
2015-01-01
In ideal MHD, shear Alfv\\'{e}n eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfv\\'{e}n continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfv\\'{e}n eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. ...
Global Alfven eigenmodes stability in thermonuclear tokamak plasmas
International Nuclear Information System (INIS)
Relying on the good agreement observed between the gyrokinetic PENN model and the low n damping measurements from JET, the stability of Alfven eigenmodes (AE) is here predicted for reactor relevant conditions. Full non-local wave-particle power transfers are computed for the α-particles in an ITER reference equilibrium, showing that low n ≅ 2 modes are strongly damped and intermediate n ≅ 12 with a global radial extension are stable with a damping rate γ/ω ≅ 0.02. Even though an excitation of α-particle driven instabilities remains in principle possible, this study suggests that realistic operation scenarii exist where all the AEs of global character are stable. (author)
Reversed shear Alfven eigenmode stabilization by localized electron cyclotron heating
Energy Technology Data Exchange (ETDEWEB)
Van Zeeland, M A; Hyatt, A W; Lohr, J; Petty, C C [General Atomics, PO Box 85608 San Diego, CA 92186-5608 (United States); Heidbrink, W W [University of California-Irvine, Irvine, CA 92697 (United States); Nazikian, R; Solomon, W M; Gorelenkov, N N; Kramer, G J [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Austin, M E [University of Texas-Austin, Austin, TX 78712 (United States); Berk, H L [Institute for Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States); Holcomb, C T; Makowski, M A [Lawrence Livermore National Laboratory, Livermore, CA (United States); McKee, G R [University of Wisconsin-Madison, Madison, WI 53726 (United States); Sharapov, S E [Euratom/UKAEA Fusion Association, Culham, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Rhodes, T L [University of California-Los Angeles, Los Angeles, California, 90095 (United States)], E-mail: vanzeeland@fusion.gat.com
2008-03-15
Reversed shear Alfven eigenmode (RSAE) activity in DIII-D is stabilized by electron cyclotron heating (ECH) applied near the minimum of the magnetic safety factor (q{sub min}) in neutral beam heated discharges with reversed-magnetic shear. The degree of RSAE stabilization, fast ion density and the volume averaged neutron production (S{sub n}) are highly dependent on ECH deposition location relative to q{sub min}. While discharges with ECH stabilization of RSAEs have higher S{sub n} and more peaked fast ion profiles than discharges with significant RSAE activity, neutron production remains strongly reduced (up to 60% relative to TRANSP predictions assuming classical fast ion transport) even when RSAEs are stabilized.
Recent progress of nonlinear simulation on the toroidal Alfven eigenmode
International Nuclear Information System (INIS)
Linear and nonlinear particle-magnetohydrodynamic (MHD) simulation codes are developed to study interactions between energetic ions and MHD modes. Energetic alpha particles with a slowing-down distribution are considered and the behavior of n=2 toroidal Alfven eigenmodes (TAE modes) is investigated with the parameters pertinent to the present large tokamaks. The linear simulation reveals the resonance condition between alpha particles and TAE mode. In the nonlinear simulation two n=2 TAE modes are destabilized and alpha particle losses induced by these TAE modes take place. Counter-passing particles are lost when they cross the passing-trapped boundary as a result of the interaction with the TAE modes. They are the major part of lost particles, but trapped particles are also lost appreciably. (author)
Evolution of toroidal Alfven eigenmode instability in TFTR
International Nuclear Information System (INIS)
The nonlinear behavior of the Toroidal Alfven Eigenmode (TAE) driven unstable by energetic ions in TFTR is studied. The evolution of instabilities can take on several scenarios: a single mode or several modes can be driven unstable at the same time, the spectrum can be steady or pulsating and there can be negligible or anomalous loss associated with the instability. This paper presents a comparison between experimental results and recently developed nonlinear theory. The authors find many features observed in experiment are compatible with the consequences of the nonlinear theory. Examples include the structure of the saturated pulse that emerges from the onset of instability of a single mode and the decrease but persistence of TAE signals when the applied rf power is reduced or shut off
Evolution of toroidal Alfven eigenmode instability in TFTR
Energy Technology Data Exchange (ETDEWEB)
Wong, K.L.; Majeski, R.; Petrov, M. [Princeton Univ., NJ (United States). Plasma Physics Lab.] [and others
1996-07-01
The nonlinear behavior of the Toroidal Alfven Eigenmode (TAE) driven unstable by energetic ions in TFTR is studied. The evolution of instabilities can take on several scenarios: a single mode or several modes can be driven unstable at the same time, the spectrum can be steady or pulsating and there can be negligible or anomalous loss associated with the instability. This paper presents a comparison between experimental results and recently developed nonlinear theory. The authors find many features observed in experiment are compatible with the consequences of the nonlinear theory. Examples include the structure of the saturated pulse that emerges from the onset of instability of a single mode and the decrease but persistence of TAE signals when the applied rf power is reduced or shut off.
Damping of kinetic Alfven eigenmodes in tokamak plasmas
International Nuclear Information System (INIS)
The ability to predict the stability of fast-particle-driven Alfven eigenmodes in burning fusion plasmas requires a detailed understanding of the dissipative mechanisms that damp these modes. In order to address this question, the linear gyro-kinetic, electromagnetic code LIGKA is employed to investigate their behaviour in realistic tokamak geometry. LIGKA is based on an eigenvalue formulation and self-consistently calculates the coupling of large-scale MHD modes to gyro-radius scale length kinetic Alfven waves. It uses the drift-kinetic HAGIS code to accurately describe the unperturbed particle orbits in general geometry. In addition, a newly developed antenna-like version of LIGKA allows for a frequency scan, analogous to an external antenna. With these tools the properties of the kinetically modified TAE in or near the gap (KTAE, radiative damping or 'tunnelling') and its coupling to the continuum close to the edge are numerically analysed. The results are compared with previous calculations based on fluid and other gyro-kinetic models. Also first linear calculations on cascade modes are presented. (author)
Observation of compressional Alfven eigenmodes (CAE) in a conventional tokamak
International Nuclear Information System (INIS)
Fast-ion instabilities with frequencies somewhat below the ion cyclotron frequency occur frequently in spherical tokamaks such as the National Spherical Torus Experiment (NSTX). NSTX and the DIII-D tokamak are nearly ideal for fast-ion similarity experiments, having similar neutral beams, fast-ion to Alfven speed vf/vA, fast-ion pressure, and shape of the plasma but with a factor of two difference in major radius. When DIII-D is operated at low field (0.6 T), compressional Alfven eigenmode (CAE) instabilities appear that closely resemble the NSTX instabilities. In particular, the mode frequencies, polarization and beam-energy threshold are nearly identical to NSTX. CAE in high-field discharges and emission at cyclotron harmonics are also observed. As on NSTX, the basic stability properties are consistent with the idea that the instability is driven by anisotropy in the fast-ion velocity distribution and is damped predominantly by Landau damping of electrons. The results suggest that these modes might be excited in ITER
Theory and observations of high frequency Alfven Eigenmodes in low aspect ratio plasma
International Nuclear Information System (INIS)
New observations of sub-cyclotron frequency instabilities in low aspect ratio plasmas in the National Spherical Torus experiment (NSTX) are reported, The frequencies of observed instabilities scale with the characteristic Alfven velocity of the plasma. A theory of localized Compressional Alfven Eigenmodes (CAE) and Global shear Alfven Eigenmodes (GAE) in low aspect ratio plasmas is presented to explain the observed high frequency instabilities. CAE's/GE's are driven by the velocity space gradient of energetic super-Alfvenic beam ions via Doppler shifted cyclotron resonances. Properties of such instabilities are investigated. (author)
Destabilization of Alfven eigenmodes by fast particles in W7-AS
Energy Technology Data Exchange (ETDEWEB)
Zegenhagen, S.
2006-02-15
In the present thesis, a systematic study of beam driven Alfven eigenmodes in high-density and low-temperature plasmas of the W7-AS stellarator is performed. The goal of this thesis is twofold: (I) identification and description of fast particle driven Alfven instabilities in W7-AS, and (II) study of energetic particle losses induced by Alfven instabilities. A total of 133 different Alfven eigenmodes is studied in discharges from different experimental campaigns. The discharges are characterized by high density, n{sub e}=5 x 1019 m{sup -3} to 2.5 x 1020 m{sup -3} at relatively low temperatures of T{sub e}=T{sub i}=150..600 eV. Additional 13 events are found to have frequencies inside the EAE gap and could possibly be EAEs. Evidence for high-frequency Alfven eigenmodes (mirror- and helicity-induced Alfven eigenmodes) is seen, but can not be proven rigorously due to uncertain mode numbers and the complexity of the Alfven continuum. The remaining 41 Alfven eigenmodes can not be classified to be one of the above cases. (orig.)
Destabilization of Alfven eigenmodes by fast particles in W7-AS
International Nuclear Information System (INIS)
In the present thesis, a systematic study of beam driven Alfven eigenmodes in high-density and low-temperature plasmas of the W7-AS stellarator is performed. The goal of this thesis is twofold: (I) identification and description of fast particle driven Alfven instabilities in W7-AS, and (II) study of energetic particle losses induced by Alfven instabilities. A total of 133 different Alfven eigenmodes is studied in discharges from different experimental campaigns. The discharges are characterized by high density, ne=5 x 1019 m-3 to 2.5 x 1020 m-3 at relatively low temperatures of Te=Ti=150..600 eV. Additional 13 events are found to have frequencies inside the EAE gap and could possibly be EAEs. Evidence for high-frequency Alfven eigenmodes (mirror- and helicity-induced Alfven eigenmodes) is seen, but can not be proven rigorously due to uncertain mode numbers and the complexity of the Alfven continuum. The remaining 41 Alfven eigenmodes can not be classified to be one of the above cases. (orig.)
Existence of Weakly Damped Kinetic Alfven Eigenmodes in Reversed Shear Tokamak
Energy Technology Data Exchange (ETDEWEB)
N. N. Gorelenkov
2008-08-12
A kinetic theory of weakly damped Alfven Eigenmode (AE) solutions strongly interacting with the continuum is developed for tokamak plasmas with reversed magnetic shear. We show that the ideal MHD model is not sufficient for the eigenmode solutions if the standard causality condition bypass rule is applied. Finite Larmor radius effects are required, which introduce multiple kinetic subeigenmodes and collisionless radiative damping. The theory explains the existence of experimentally observed Alfvenic instabilities with frequencies sweeping down and reaching their minimum (bottom).
Simulation study of energetic ion transport due to Alfven eigenmodes in LHD plasma
International Nuclear Information System (INIS)
The creation of holes and clumps in an energetic ion energy spectrum associated with Alfven eigenmodes was examined using the neutral particle analyzer (NPA) on the LHD shot no.47645. The difference in slowing-down times between the holes and clumps suggested that the energetic ions were transported over 10% of the plasma minor radius. The spatial profile and frequency of the Alfven eigenmodes were analyzed with the AE3D code. The phase space structures of the energetic ions on the NPA line-of-sight were investigated with Poincare plots, where an oscillating Alfven eigenmode was employed for earth plot. The phase space regions trapped by the Alfven eigenmodes appeared as islands in the Poincare plots. The radial width of the islands corresponded to the transport distance of the energetic ions. Since island width depends on Alfven eigenmode amplitude, it was found that Alfven eigenmodes with amplitude δBr/B - 10-3 transported energetic ions over 10% of the minor radius. (author)
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
Energy Technology Data Exchange (ETDEWEB)
Batha, S.H.; Levinton, F.M. [Fusion Physics and Technology, Torrance, CA (United States); Spong, D.A. [Oak Ridge National Lab., TN (United States)] [and others
1995-07-01
Experiments to destabilize the Toroidicity-induced Alfven Eigenmode (TAE) by energetic alpha particles were performed on the Tokamak Fusion Test Reactor using deuterium and tritium fuel. To decrease the alpha particle pressure instability threshold, discharges with an elevated value of q(0) > 1.5 were used. By raising q(0), the radial location of the low toroidal-mode-number TAE gaps moves toward the magnetic axis and into alignment with the region of maximum alpha pressure gradient, thereby (in theory) lowering the value of {beta}{sub {alpha}}(0) required for instability. No TAE activity was observed when the central alpha particle {beta}{sub {alpha}} reached 0.08% in a discharge with fusion power of 2.4 MW. Calculations show that the fusion power is within a factor of 1.5 to 3 of the instability threshold.
Beam Anisotropy Effect on Alfven Eigenmode Stability in ITER-like Plasma
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov; H.L. Berk; R.V. Budny
2004-08-18
This work studies the stability of the toroidicity-induced Alfven Eigenmodes (TAE) in the proposed ITER burning plasma experiment, which can be driven unstable by two groups of energetic particles, the 3.5-MeV {alpha}-particle fusion products and the tangentially injected 1-MeV beam ions. Both species are super-Alfvenic but they have different pitch-angle distributions and the drive for the same pressure gradients is typically stronger from co-injected beam ions as compared with the isotropically distributed {alpha}-particles. This study includes the effect of anisotropy of the beam-ion distribution function on TAE growth rate directly via the additional velocity space drive and indirectly in terms of the enhanced effect of the resonant particle phase space density. For near parallel injection, TAEs are marginally unstable if the injection aims at the plasma center where the ion Landau damping is strong, whereas with the off-axis neutral-beam injection the instability is stronger with the growth rate near 0.5% of TAE mode frequency. In contrast, for perpendicular beam injection TAEs are predicted to be stabilized in nominal ITER discharges. In addition, the effect of TAEs on the fast-ion beta profiles is evaluated on the bases of a quasi-linear diffusion model which makes use of analytic expressions for the local growth and damping rates. These results illustrate the parameter window that is available for plasma burn when TAE modes are excited.
Calculation of continuum damping of Alfv\\'en eigenmodes in 2D and 3D cases
Bowden, G W; Könies, A
2015-01-01
In ideal MHD, shear Alfv\\'{e}n eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfv\\'{e}n continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfv\\'{e}n eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD code CKA . ...
Tholerus, Emmi; Hellsten, Torbjörn
2016-01-01
FOXTAIL is a new hybrid magnetohydrodynamic-kinetic code used to describe interactions between energetic particles and Alfv\\'en eigenmodes in tokamaks with realistic geometries. The code simulates the nonlinear dynamics of the amplitudes of individual eigenmodes and of a set of discrete markers in five-dimensional phase space representing the energetic particle distribution. Action-angle coordinates of the equilibrium system are used for efficient tracing of energetic particles, and the particle acceleration by the wave fields of the eigenmodes is Fourier decomposed in the same angles. The eigenmodes are described using temporally constant eigenfunctions with dynamic complex amplitudes. Possible applications of the code are presented, e.g., making a quantitative validity evaluation of the one-dimensional bump-on-tail approximation of the system. Expected effects of the fulfillment of the Chirikov criterion in two-mode scenarios have also been verified.
Sensitivity of alpha-particle-driven Alfven eigenmodes to q-profile variation in ITER scenarios
Rodrigues, P; Fazendeiro, L; Ferreira, J; Coelho, R; Nabais, F; Borba, D; Polevoi, N F Loureiro A R; Pinches, S D; Sharapov, S E
2016-01-01
An hybrid ideal-MHD/drift-kinetic approach to assess the stability of alpha-particle-driven Alfven eigenmodes in burning plasmas is used to show that certain foreseen ITER scenarios, namely the $I_\\mathrm{p} = 15$ MA baseline scenario with very low and broad core magnetic shear, are sensitive to small changes in the background magnetic equilibrium. Slight perturbations (of the order of 1%) in the total plasma current are seen to cause large variations in the growth rate, toroidal mode number, and radial location of the most unstable eigenmodes found. The observed sensitivity is shown to proceed from the very low magnetic shear values attained throughout the plasma core.
Subcyclotron Instability of Alfven Eigenmodes due to Energetic Ions in Low Aspect Ratio Plasmas
International Nuclear Information System (INIS)
High-frequency modes with frequencies below the fundamental cyclotron frequency of thermal ions were observed in the National Spherical Torus Experiment (NSTX). Based on the measured spectrum of high-frequency modes they are identified as Compressional Alfven Eigenmodes (CAEs) and Global Alfven Eigenmodes (GAEs). CAEs have similar time evolution as plasma parameters change, while GAEs may intersect due to q-profile relaxation. A theory has been developed to study the properties of these modes. Both types of instabilities are driven by the tangential neutral-beam injection in NSTX. Beam ions excite CAEs/GAEs through the Doppler-shifted cyclotron resonance. The main source for the drive is the velocity space anisotropy of the beam ion distribution function. Simulations of the effect CAEs/GAEs may have on plasma ions indicate that these modes may provide a channel for efficient energy transfer from fast ions directly to thermal ions
Numerical simulation of core-localized aloha-driven Alfven eigenmodes in tokamaks
International Nuclear Information System (INIS)
The stability of core-localized toroidicity-induced alpha-driven Alfven eigenmodes (TAE) is investigated numerically for tokamak equilibria with circular flux surfaces. It is demonstrated that the TAE mode growth rate is strongly affected by the tokamak magnetic field geometry (i.e. Shafranov shift of the magnetic axis) as well as by the ripple induced transport of high energetic alpha particles. (author)
International Nuclear Information System (INIS)
Instabilities of the Alfven eigenmodes (AEs) that can be driven by circulating energetic ions in optimized stellarators of the Wendelstein line (Helias configurations) are considered. It is stressed that the Alfv‚n instabilities in stellarators may considerably differ from those in tokamaks because specific Alfv‚n eigenmodes and specific resonances of the wave-particle interaction appear when magnetic configurations are non-axisymmetric. An important role of the continuum damping in low-shear stellarators is revealed. Aimed to calculate the continuum damping, a set of resistive magnetohydrodynamic (MHD) equations, which generalize the ideal MHD AE equations obtained in Kolesnichenko et al (Kolesnichenko Ya.I. et al 2001 Phys. Plasmas 8 491), is derived. The derived equations are solved numerically to investigate the damping of the AEs of global character in a Helias reactor. (author)
Effects of energetic particles on zonal flow generation by toroidal Alfven eigenmode
Qiu, Zhiyong; Zonca, Fulvio
2016-01-01
Generation of zonal ow (ZF) by energetic particle (EP) driven toroidal Alfven eigenmode (TAE) is investigated using nonlinear gyrokinetic theory. It is found that, nonlinear resonant EP contri- bution dominates over the usual Reynolds and Maxwell stresses due to thermal plasma nonlinear response. ZF can be forced driven in the linear growth stage of TAE, with the growth rate being twice the TAE growth rate. The ZF generation mechanism is shown to be related to polarization induced by resonant EP nonlinearity. The generated ZF has both the usual meso-scale and micro- scale radial structures. Possible consequences of this forced driven ZF on the nonlinear dynamics of TAE are also discussed.
Anomalous Electron Transport Due to Multiple High Frequency Beam Ion Driven Alfven Eigenmode
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N. N.; Stutman, D.; Tritz, K.; Boozer, A.; Delgardo-Aparicio, L.; Fredrickson, E.; Kaye, S.; White, R.
2010-07-13
We report on the simulations of recently observed correlations of the core electron transport with the sub-thermal ion cyclotron frequency instabilities in low aspect ratio plasmas of the National Spherical Torus Experiment (NSTX). In order to model the electron transport of the guiding center code ORBIT is employed. A spectrum of test functions of multiple core localized Global shear Alfven Eigenmode (GAE) instabilities based on a previously developed theory and experimental observations is used to examine the electron transport properties. The simulations exhibit thermal electron transport induced by electron drift orbit stochasticity in the presence of multiple core localized GAE.
Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging
International Nuclear Information System (INIS)
Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.
Fast Ion Induced Shearing of 2D Alfven Eigenmodes Measured by Electron Cyclotron Emission Imaging
Energy Technology Data Exchange (ETDEWEB)
Tobias, Ben [University of California, Davis; Classen, I.G.J. [FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein, The Netherlands; Domier, C. W. [University of California, Davis; Heidbrink, W. [University of California, Irvine; Luhmann, N.C. [University of California, Davis; Nazikian, Raffi [Princeton Plasma Physics Laboratory (PPPL); Park, H.K. [Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea; Spong, Donald A [ORNL; Van Zeeland, Michael [General Atomics
2011-01-01
Two-dimensional images of electron temperature perturbations are obtained with electron cyclotron emission imaging (ECEI) on the DIII-D tokamak and compared to Alfven eigenmode structures obtained by numerical modeling using both ideal MHD and hybrid MHD-gyrofluid codes. While many features of the observations are found to be in excellent agreement with simulations using an ideal MHD code (NOVA), other characteristics distinctly reveal the influence of fast ions on the mode structures. These features are found to be well described by the nonperturbative hybrid MHD-gyrofluid model TAEFL.
Predications and Observations of Global Beta-induced Alfven-acoustic Modes in JET and NSTX
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov, et. al.
2008-10-21
In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfven-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.
Predictions and observations of global beta-induced Alfven-acoustic modes in JET and NSTX
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N N [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Berk, H L [Institute for Fusion Studies, University of Texas, Austin, TX 78712 (United States); Crocker, N A [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Fredrickson, E D [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kaye, S [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Kubota, S [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Park, H [Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States); Peebles, W [Institute of Plasma and Fusion Research, University of California, Los Angeles, CA 90095-1354 (United States); Sabbagh, S A [Department of Applied Physics, Columbia University, New York, NY 10027-6902 (United States); Sharapov, S E [Euroatom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB (United Kingdom); Stutmat, D [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Tritz, K [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Levinton, F M [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States); Yuh, H [Nova Photonics, One Oak Place, Princeton, NJ 08540 (United States)
2007-12-15
In this paper we report on observations and interpretations of a new class of global MHD eigenmode solutions arising in gaps in the low frequency Alfven-acoustic continuum below the geodesic acoustic mode frequency. These modes have been just reported (Gorelenkov et al 2007 Phys. Lett. 370 70-7) where preliminary comparisons indicate qualitative agreement between theory and experiment. Here we show a more quantitative comparison emphasizing recent NSTX experiments on the observations of the global eigenmodes, referred to as beta-induced Alfven-acoustic eigenmodes (BAAEs), which exist near the extrema of the Alfven-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes may shift as the safety factor, q, profile relaxes. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta <2% as well as in NSTX plasmas at relatively high beta >20%. In NSTX plasma observed magnetic activity has the same properties as predicted by theory for the mode structure and the frequency. Found numerically in NOVA simulations BAAEs are used to explain the observed properties of relatively low frequency experimental signals seen in NSTX and JET tokamaks.
Perturbative Study of Energetic Particle Redistribution by Alfven Eigenmodes in ITER
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov and R.B. White
2012-10-29
The modification of particle distributions by magnetohydrodynamic modes is an important topic for magnetically confined plasmas. Low amplitude modes are known to be capable of producing significant modification of injected neutral beam profiles. Flattening of a distribution due to phase mixing in an island or due to portions of phase space becoming stochastic is a process extremely rapid on the time scale of an experiment. In this paper we examine the effect of toroidal Alfven eigenmodes (TAE) and reversed shear Alfven eigenmodes (RSAE) in ITER on alpha particle and injected beam distributions using theoretically predicted mode amplitudes. It is found that for the equilibrium of a hybrid scenario even at ten times the predicted saturation level the modes have negligible effect on these distributions. A strongly reversed shear (or advanced) scenario, having a spectrum of modes that are much more global, is somewhat more susceptible to induced loss due to mode resonance, with alpha particle losses of over one percent with predicted amplitudes and somewhat larger with the assistance of toroidal field ripple. The elevated q profile contributes to stronger TAE (RSAE) drive and more unstable modes. An analysis of the existing mode-particle resonances is carried out to determine which modes are responsible for the profile modification and induced loss. We find that losses are entirely due to resonance with the counter-moving and trapped particle populations, with co-moving passing particles participating in resonances only deep within the plasma and not leading to loss.
Simulation study of interaction between energetic ions and Alfven eigenmodes in LHD
International Nuclear Information System (INIS)
Interaction between energetic ions and Alfven eigenmodes (AE modes) in LHD was investigated with numerical approaches. The spatial profile and frequency of the AE modes in an LHD plasma no.47645, where the creation of holes and clumps in the energetic ion energy spectrum associated with AE modes was observed with the neutral particle analyzer (NPA), were analyzed with the AE3D code. The phase space structures of the energetic ions on the NPA line-of-sight were investigated with the Poincare plots where an oscillating AE mode for each plot is employed. The radial width of the phase space regions trapped by the AE modes corresponds to the transport distance of energetic ions. As island width depends on AE mode amplitude, it was found that AE mode amplitude of δBr/B - 10-3 is consistent with the energetic-ion transport over 10% of the minor radius that is suggested by the difference in slowing-down time between the holes and clumps observed with the NPA in the LHD experiment. Furthermore, a numerical code which simulates the time evolution of energetic particles and AE mode amplitude and phase in a self-consistent way has been newly developed for three-dimensional equilibria such as LHD. Alfven eigenmode bursts in LHD plasma were simulated with neutral-beam injection and collisions taken into account. (author)
Non-linear study of fast particle excitation of global Alfven eigenmodes during ICRH
International Nuclear Information System (INIS)
Full text: Fast ions created by ICRH have been proposed for simulating alpha particle heating. In order to extrapolate results regarding excitation of global Alfven eigenmodes to that of thermonuclear alpha particles it is important to understand the differences between excitation by ICRH and by thermonuclear alpha particles. ICRH does not only produce strong anisotropic distribution functions of the resonant ion species compared to the nearly isotropic one of thermonuclear alpha particles, but also decorrelates the interactions between the high-energy ions and the global Alfven eigenmode. In absence of decorrelation the resonant ions will make superadiabatic oscillations in energy. The decorrelation caused by collisions and RF interactions leads to an effective broadening of the MHD resonant region hence increasing the extent of the energy transport region in phase space. The decorrelations also affect the growth rate and the amplitude of the saturation level. ICRH decorrelates the MHD interactions and pushes ions in and out of resonance with the Alfven wave leading to enhanced excitation or damping of the mode. The decorrelation by Coulomb collisions decreases with energy and is more important for particles with low energy, whereas the decorrelation by ICRH becomes more important for high-energy particles. A method to calculate the distribution function of the resonant ions and amplitude of the global Alfven wave self-consistently during ICRH has been developed and implemented in the SELFO- code. The SELFO code consists of the orbit averaged Monte Carlo code FIDO for calculating the distribution function of the heated ions and the global wave code LION for calculating the wave field for ICRF heating. Self-consistent calculations of the ICRF wave field and distribution function is carried out by solving the wave field in LION with a dielectric tensor calculated from the global distribution function obtained with the FIDO code. The wave field of the global Alfven
International Nuclear Information System (INIS)
The National Spherical Torus Experiment (NSTX, (M. Ono et al., Nucl. Fusion 40, 557 (2000))) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfvenic, with velocities 1 fast/vAlfven < 5. This provides a strong drive for toroidicity-induced Alfven eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (∼<30%) fast ion losses over ∼ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
Nonlinear Studies of β-Induced Alfven Eigenmode Driven by Energetic Particles in Fusion Plasmas
International Nuclear Information System (INIS)
Full text: The β-induced Alfven eigenmodes (BAEs) driven by energetic particles (EPs) are observed in early and recent experiments, which can lead to radial redistribution of EPs and, consequently, anomalous EP transport. In the present work, we have employed the nonlinear hybrid magnetohydrodynamic gyro-kinetic code (XHMGC), and investigated the excitation and nonlinear saturation of BAE via transit resonance with slowing-down beam ions. Saturation is found to be characterized by upward frequency chirping and symmetry breaking between co- and counter passing particles, which can be understood as the evidence of radial resonance detuning. Further investigations on the scaling of the saturation amplitude with the growth rate is also found to be consistent with radial resonance detuning due to the radial non-uniformity and mode structure. (author)
Experimental study of toroidicity-induced Alfven eigenmode (TAE) stability at high q(0)
International Nuclear Information System (INIS)
Experiments to destabilize the Toroidicity-induced Alfven Eigenmode (TAE) by energetic alpha particles were performed on the Tokamak Fusion Test Reactor using deuterium and tritium fuel. To decrease the alpha particle pressure instability threshold, discharges with an elevated value of q(0) > 1.5 were used. By raising q(0), the radial location of the low toroidal-mode-number TAE gaps moves toward the magnetic axis and into alignment with the region of maximum alpha pressure gradient, thereby (in theory) lowering the value of βα(0) required for instability. No TAE activity was observed when the central alpha particle βα reached 0.08% in a discharge with fusion power of 2.4 MW. Calculations show that the fusion power is within a factor of 1.5 to 3 of the instability threshold
International Nuclear Information System (INIS)
The spectrum of Compressional Alfven Eigenmodes (CAE) driven by phase space gradient measured in NSTX and DIII-D plasmas is analyzed numerically for the first time. Advanced diagnostic capabilities made it possible to measure single mode polarization and toroidal mode numbers, which unambiguously identifies studied modes to be of compressional branch. CAE modes form the discrete spectrum with each mode having three (quantum) mode numbers (M, S, n), where M, S, and n are poloidal, radial and toroidal mode numbers, respectively. CAE mode frequency splitting corresponding to change of each of these mode numbers seem to be observed in experiments and is consistent with our numerical analysis. CAE mode structure is computed to be localized in both radial and poloidal directions and is shown to be consistent with the internal reflectometer diagnostic data. (author)
Stability analysis of toroidicity-induced Alfven eigenmodes in TFTR DT experiments
International Nuclear Information System (INIS)
The toroidicity-induced Alfvin eigenmodes (TAE) with radially extended structure are found to be stable in the Tokamak Fusion Test Reactor Deuterium-Tritium plasmas. A core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta, which can be destabilized by energetic alpha particles on TFTR. With additional instability drive from fast minority ions powered by ICRH, both the global and the core localized TAE modes can be readily destabilized
Simulation study of beam ion loss due to Alfven eigenmode bursts
International Nuclear Information System (INIS)
Recurrent bursts of toroidicity-induced Alfven eigenmodes (TAE) are studied using a self-consistent simulation model. Bursts of beam ion losses observed in the neutral beam injection experiment at the Tokamak Fusion Test Reactor [K. L. Wong et al., Phys. Rev. Lett. 66, 1874 (1991)] are reproduced using the experimental parameters. It is found that synchronized TAE bursts take place at regular time intervals of 2.5 ms, which is fairly close to the experimental value of 2.2 ms. The stored beam energy saturates at 10% of that of the classical slowing-down distribution. This is consistent with an important experimental aspect that the beam confinement time is much shorter than the collisional slowing-down time. The stored beam energy drop associated with each burst has a modulation depth of 20% which is comparable to the inferred experimental value of 7%. This is the first simulation that reproduces all of these experimental aspects. The beam ion distribution hovers around a marginal stability state. Test particle analysis demonstrates that the disappearance of KAM surfaces in a coordinate system co-moving with each eigenmode leads to beam ion loss. (author)
Measurement of the effective plasma ion mass in large tokamaks using Global Alfven Eigenmodes
International Nuclear Information System (INIS)
The ratio in the centre of a tokamak plasma. One of the simpler measurements put forward in the past is the interpretation of the MHD spectrum in the frequency range of the Global Alfven Eigenmodes (GAE). However, the frequencies of these modes do not depend only on the plasma mass, but are also quite strongly dependent on the details of the current and density profiles, creating a problem of deconvolution of the estimate of the plasma mass from an implicit relationship between several measurable plasma parameters and the detected eigenmode frequencies. In view of the lack of competitive diagnostics, this method has been revisited to assess its likely precision for the JET tokamak. Our results show that the low-n GAE modes are sometimes too close to the continuum edge to be detectable and that the interpretation of the GAE spectrum is therefore rendered less direct than had been hoped. However, information on the effective plasma ion mass is still available in the detectable modes and we present a statistical study on the precision with which this quantity could be estimated from the GAE spectrum on JET, including other directly measured or simply available plasma parameters. (author) 5 figs., 3 tabs., 10 refs
Alfven eigenmode stability and fast ion loss in DIII-D and ITER reversed magnetic shear plasmas
Energy Technology Data Exchange (ETDEWEB)
Van Zeeland, Michael [General Atomics; Gorelenkov, Nikolai [Princeton Plasma Physics Laboratory (PPPL); Heidbrink, W. [University of California, Irvine; Kramer, G. [Princeton Plasma Physics Laboratory (PPPL); Spong, Donald A [ORNL; Austin, M. E. [University of Texas, Austin; Fisher, R K [General Atomics, San Diego; Munoz, M G [Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Garching, Germany; Gorelenkova, M. [Princeton Plasma Physics Laboratory (PPPL); Luhmann, N.C. [University of California, Davis; Murakami, Masanori [ORNL; Nazikian, Raffi [Princeton Plasma Physics Laboratory (PPPL); Park, J. M. [Oak Ridge National Laboratory (ORNL); Tobias, Ben [University of California, Davis; White, R. [Princeton Plasma Physics Laboratory (PPPL)
2012-01-01
Neutral beam injection into reversed-magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including toroidicity-induced Alfven eigenmodes (TAEs) and reversed shear Alfven eigenmodes (RSAEs). With measured equilibrium profiles as inputs, the ideal MHD code NOVA is used to calculate eigenmodes of these plasmas. The postprocessor code NOVA-K is then used to perturbatively calculate the actual stability of the modes, including finite orbit width and finite Larmor radius effects, and reasonable agreement with the spectrum of observed modes is found. Using experimentally measured mode amplitudes, fast ion orbit following simulations have been carried out in the presence of the NOVA calculated eigenmodes and are found to reproduce the dominant energy, pitch and temporal evolution of the losses measured using a large bandwidth scintillator diagnostic. The same analysis techniques applied to a DT 8 MA ITER steady-state plasma scenario with reversed-magnetic shear and both beam ion and alpha populations show Alfven eigenmode instability. Both RSAEs and TAEs are found to be unstable with maximum growth rates occurring for toroidal mode number n = 6 and the majority of the drive coming from fast ions injected by the 1MeV negative ion beams. AE instability due to beam ion drive is confirmed by the non-perturbative code TAEFL. Initial fast ion orbit following simulations using the unstable modes with a range of amplitudes (delta B/B = 10(-5)-10(-3)) have been carried out and show negligible fast ion loss. The lack of fast ion loss is a result of loss boundaries being limited to large radii and significantly removed from the actual modes themselves.
International Nuclear Information System (INIS)
The stability of the Global Alfven Eigenmodes is investigated in the presence of super-Alfvenic energetic particles, such as the fusion-product alpha particles in an ignited deuterium-tritium tokamak plasma. Alpha particles tend to destabilize these modes when ω*α > ωA, where ωA is the shear-Alfven modal frequency and ω*α is the alpha particle diamagnetic drift frequency. This destabilization due to alpha particles is found to be significantly enhanced when the alpha particles are modeled with a slowing-down distribution function rather than with a Maxwellian. However, previously neglected electron damping due to the magnetic curvature drift is found to be comparable in magnitude to the destabilizing alpha particle term. Furthermore, the effects of toroidicity are also found to be stabilizing, since the intrinsic toroidicity induces poloidal mode coupling, which enhances the parallel electron damping from the sideband shear-Alfven Landau resonance. In particular, for the parameters of the proposed Compact Ignition Tokamak, the Global Alfven Eigenmodes are found to be completely stabilized by either the electron damping that enters through the magnetic curvature drift or the damping introduced by finite toroidicity. 29 refs., 8 figs., 1 tab
International Nuclear Information System (INIS)
In a circular cylindrical geometry, the author solves a fourth-order set of differential equations numerically for the perturbed fields Eτ and Eperpendicular. The model takes into account the equilibrium current, magnetic shear, finite ω/ωc1 effect, mode conversion effects like finite ion gyroradius and electron inertia, and various dissipative mechanisms such as electron Landau and collisional damping, and minority fundamental and majority second harmonic cyclotron absorption. To illustrate the results, the author plots the perturbed electric fields and the energy absorbed by each species. He first examines cold plasma surface Alfven eigenmodes analytically and numerically in a pure plasma. The motivation for this work is to investigate how to avoid the undesirable edge absorption and introduce the methods for the study of impurity effects. In the two-species plasmas, he considers three special examples: (1) minority oxygen in hydrogen in PRETEXT, (2) minority T or H in deuterium in TFTR. He adopts two models: (i) a radially varying minority charge, or (ii) a radially varying magnetic field to investigate the minority gyroresonance heating. The model (ii) is used to examine these three examples. But the model (i) is only applied to the first one. In model (i), it is found that surface modes can induce the eigenmodes and dissipate substantial energy near the hybrid layer in the interior. Some cases analytically manageable are given an interpretation of why there is large or small energy deposition in this layer. It is shown that this strongly depends on poloidal mode numbers, minority concentrations, and minority charge profiles
Figueiredo, A C A; Borba, D; Coelho, R; Fazendeiro, L; Ferreira, J; Loureiro, N F; Nabais, F; Pinches, S D; Polevoi, A R; Sharapov, S E
2016-01-01
The linear stability of Alfv\\'en eigenmodes in the presence of fusion-born alpha particles is thoroughly assessed for two variants of an ITER baseline scenario, which differ significantly in their core and pedestal temperatures. A systematic approach is used that considers all possible eigenmodes for a given magnetic equilibrium and determines their growth rates due to alpha-particle drive and Landau damping on fuel ions, helium ashes and electrons. This extensive stability study is efficiently conducted through the use of a specialized workflow that profits from the performance of the hybrid MHD drift-kinetic code $\\mbox{CASTOR-K}$ (Borba D. and Kerner W. 1999 J. Comput. Phys. ${\\bf 153}$ 101; Nabais F. ${\\it et\\,al}$ 2015 Plasma Sci. Technol. ${\\bf 17}$ 89), which can rapidly evaluate the linear growth rate of an eigenmode. It is found that the fastest growing instabilities in the aforementioned ITER scenario are core-localized, low-shear toroidal Alfv\\'en eigenmodes. The largest growth-rates occur in the s...
Sears, Stephanie; Anderson, Jay; Capecchi, William; Bonofiglo, Phillip; Kim, Jungha
2015-11-01
Alfven wave dissipation is an important mechanism behind anomalous ion heating, both in astrophysical and reversed-field pinch (RFP) plasma systems. Additionally, the damping rate has implications for the stability of energetic particle driven modes (EPMs) and their associated nonlinear dynamics and fast ion transport, which are crucial topics for any burning plasma reactor. With a 1 MW neutral beam injector on the MST RFP, a controlled set of EPMs and Alfvenic eigenmodes can be driven in this never-before-probed region of strong magnetic shear and weak externally applied magnetic field. The decay time of the average of 100s of reproducible bursts is computed for different equilibrium profiles. In this work, we report initial measurements of Alfvenic damping rates with varied RFP equilibria (including magnetic shear and flow shear) and the effects on fast ion transport. This research is supported by DOE and NSF.
Wang, Ge; Berk, H. L.
2011-10-01
The frequency chirping signal arising from spontaneous a toroidial Alfven eigenmode (TAE) excited by energetic particles is studied for both numerical and analytic models. The time-dependent numerical model is based on the 1D Vlasov equation. We use a sophisticated tracking method to lock onto the resonant structure to enable the chirping frequency to be nearly constant in the calculation frame. The accuracy of the adiabatic approximation is tested during the simulation which justifies the appropriateness of our analytic model. The analytic model uses the adiabatic approximation which allows us to solve the wave evolution equation in frequency space. Then, the resonant interactions between energetic particles and TAE yield predictions for the chirping rate, wave frequency and amplitudes vs. time. Here, an adiabatic invariant J is defined on the separatrix of a chirping mode to determine the region of confinement of the wave trapped distribution function. We examine the asymptotic behavior of the chirping signal for its long time evolution and find agreement in essential features with the results of the simulation. Work supported by Department of Energy contract DE-FC02-08ER54988.
Alfven eigenmode observations on DIII-D via two-colour CO{sub 2} interferometry
Energy Technology Data Exchange (ETDEWEB)
Zeeland, M A van [ORISE, PO Box 117, Oak Ridge, TN 37831-0117 (United States); Kramer, G J [Princeton Plasma Physics Lab., PO Box 451, Princeton, NJ 08543 (United States); Nazikian, R [Princeton Plasma Physics Lab., PO Box 451, Princeton, NJ 08543 (United States); Berk, H L [Institute of Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States); Carlstrom, T N [General Atomics, PO Box 85608, San Diego, CA 92186-9784 (United States); Solomon, W M [Princeton Plasma Physics Lab., PO Box 451, Princeton, NJ 08543 (United States)
2005-09-01
Measurements are presented of toroidicity-induced (TAEs) and reverse shear (RSAEs) Alfven eigenmodes made using the standard two-colour CO{sub 2} interferometer on DIII-D modified for increased bandwidth. Typical values of the effective line-integrated density perturbation in DIII-D are found to be d(nL)/nL {approx} 10{sup -3}, and comparisons are made with NOVA calculations as well as magnetic measurements. There is a strong difference in the measured power spectrum between vertical and radial chords through the plasma. On average, vertical views are characterized by a larger line-integrated density perturbation due to TAEs than radial chords. Radial chords, however, can be used much more reliably than vertical chords to identify the presence of RSAEs in the plasma-a result found to be due to the radially localized nature of these modes. In general, the apparent amplitude of the observed modes for both TAE and RSAE is found to be highly dependent on viewing location. (letter to the editor)
Geometrical and profile effects on toroidicity and ellipticity induced Alfven eigenmodes
International Nuclear Information System (INIS)
The wave structures, eigenfrequencies and damping rates of toroidicity and ellipticity induced Alfven eigenmodes (TAE, EAE) of low toroidal mode numbers (n) are calculated in various axisymmetric ideal MHD equilibria with the global wave finite element code LION. The importance of safety factor (q) and density (ρ) profiles on continuum damping rates is analysed. For realistic profiles several continuum gaps exist in the plasma discharge. Frequency misalignment of these gaps yields continuum damping rates γ/ω of the order of a few percent. Finite βpol lowers the TAE eigenfrequency. For β values below the Troyon limit the TAE enters the continuum and can thus be stabilized. Finite elongation allows the EAE to exist but triangularity can have a stabilizing effect through coupling to the continuum. The localization of TAE and EAE eigenfunctions is found to increase with the shear and with n. Therefore large shear, through enhanced Landau and collisional damping, is a stabilizing factor for TAE and EAE modes. (author) 16 figs., 28 refs
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Podesta, M; Crocker, N A; Fredrickson, E D; Gorelenkov, N N; Heidbrink, W W; Kubota, S; LeBlanc, B P
2011-04-26
The National Spherical Torus Experiment (NSTX, [M. Ono et al., Nucl. Fusion 40, 557 (2000)]) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfv enic, with velocities 1 < vfast=vAlfven < 5. This provides a strong drive for toroidicity-induced Alfv en eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (≤ 30%) fast ion losses over ~ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.
Kinetic Alfven solitons in a low-beta plasma
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Kinetic Alfven solitons with hot electrons and finite electron inertia in a low beta (β=8πnoT/B2G, the ratio of the kinetic to the magnetic pressure) plasma is studied analytically, with the ion motion being considered dominant through the polarization drift. Both compressive and rarefactive kinetic Alfven solitons are found to exist within a definite range of kz (the direction of propagation of the kinetic Alfven solitary waves with respect to the direction of the magnetic field) for each pair of assigned values of β and M (Mach number). Unlike in previous theoretical investigations, β appears as an explicit parameter for the kinetic Alfven solitons in this case. In addition, consideration of the electron pressure gradient is found to suppress the speed of both the Alfven solitons considerably for A (=2QM2 / βk2z, with Q the electron-to-ion mass ratio) less than unity. (Author)
The Berk-Breizman Model as a Paradigm for Energetic Particle-driven Alfven Eigenmodes
International Nuclear Information System (INIS)
The achievement of sustained nuclear fusion in magnetically confined plasma relies on efficient confinement of alpha particles. Such particles can excite instabilities in the frequency range of Alfven Eigenmodes (AEs), which significantly degrade their confinement and threatens the vacuum vessel of future reactors. In the case of an isolated single resonance, the description of AE destabilization by high-energy ions is homothetic to the so-called Berk-Breizman (BB) problem. A semi-Lagrangian simulation code, COBBLES, is developed to solve the initial-value BB problem in both perturbative (δf) and self-consistent (full-f) approaches. Two collision models are considered, namely a Krook model, and a model that includes dynamical friction (drag) and velocity-space diffusion. The nonlinear behavior of instabilities in experimentally-relevant conditions is categorized into steady-state, periodic, chaotic, and frequency-sweeping (chirping) regimes, depending on external damping rate and collision frequency. The chaotic regime is shown to extend into a linearly stable region, and a mechanism that solves the paradox formed by the existence of such subcritical instabilities is proposed. Analytic and semi-empirical laws for nonlinear chirping characteristics, such as sweeping-rate, lifetime, and asymmetry, are developed and validated. Long-time simulations demonstrate the existence of a quasi-periodic chirping regime. Although the existence of such regime stands for both collision models, drag and diffusion are essential to reproduce the alternation between major chirping events and quiescent phases, which is observed in experiments. A new method for analyzing fundamental kinetic plasma parameters, such as linear drive and external damping rate, is developed. The method, which consists of fitting procedures between COBBLES simulations and quasi-periodic chirping AE experiments, does not require any internal diagnostics. This approach is applied to Toroidicity-induced AEs
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The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) (M. Ono et al., Nucl. Fusion 40 557 (2000)). The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
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Podesta, M; Fredrickson, E D; Gorelenkov, N N; LeBlanc, B P; Heidbrink, W W; Crocker, N A; Kubota, S
2010-08-19
The effects of a sheared toroidal rotation on the dynamics of bursting Toroidicity-induced Alfven eigenmodes are investigated in neutral beam heated plasmas on the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40 557 (2000)]. The modes have a global character, extending over most of the minor radius. A toroidal rotation shear layer is measured at the location of maximum drive for the modes. Contrary to results from other devices, no clear evidence of increased damping is found. Instead, experiments with simultaneous neutral beam and radio-frequency auxiliary heating show a strong correlation between the dynamics of the modes and the instability drive. It is argued that kinetic effects involving changes in the mode drive and damping mechanisms other than rotation shear, such as continuum damping, are mostly responsible for the bursting dynamics of the modes.
Rodrigues, P; Ferreira, J; Coelho, R; Nabais, F; Borba, D; Loureiro, N F; Oliver, H J C; Sharapov, S E
2014-01-01
A systematic approach to assess the linear stability of Alfv\\'en eigenmodes in the presence of fusion-born alpha particles is described. Because experimental results for ITER are not available yet, it is not known beforehand which Alfv\\'en eigenmodes will interact more intensively with the alpha-particle population. Therefore, the number of modes that need to be considered in stability assessments becomes quite large and care must be exercised when choosing the numerical tools to work with, which must be fast and efficient. In the presented approach, all possible eigenmodes are first found after intensively scanning a suitable frequency range. Each solution found is then tested to find if its discretization over the radial grid in use is adequate. Finally, the interaction between the identified eigenmodes and the alpha-particle population is evaluated with the drift-kinetic code CASTOR-K, in order to assess their growth rates and hence their linear stability. The described approach enables one to single out t...
1.5D quasilinear model and its application on beams interacting with Alfven eigenmodes in DIII-D
Energy Technology Data Exchange (ETDEWEB)
Ghantous, K.; Gorelenkov, N. N. [Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543-0451 (United States); Berk, H. L. [Institute for Fusion Studies, University of Texas, 2100 San Jacinto Blvd., Austin, Texas 78712-1047 (United States); Heidbrink, W. W. [Department of Physics and Astronomy, University of California Irvine, Irvine, California 92697 (United States); Van Zeeland, M. A. [General Atomics, PO Box 85608, San Diego, California 92186-560 (United States)
2012-09-15
We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges no. 142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and no. 127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.
Energy Technology Data Exchange (ETDEWEB)
Weiland, Markus; Geiger, Benedikt; Bilato, Roberto; Schneider, Philip; Tardini, Giovanni; Lauber, Philipp; Ryter, Francois; Schneller, Mirjam [Max-Planck-Institut fuer Plasmaphysik, Garching (Germany); Collaboration: ASDEX Upgrade Team
2015-05-01
Fast, supra-thermal ions are created in the tokamak ASDEX Upgrade by neutral beam injection and ion cyclotron resonance heating (ICRH) and they are needed for plasma heating and current drive. A possibility to study them is the spectroscopic observation of line radiation (fast-ion D-alpha, FIDA), which emerges from charge exchange reactions. Here, the fast ions can be distinguished from the thermal particles through there strong Doppler-shift, and their radial density profile can be measured and compared to theoretical models. An analysis of the whole Doppler spectrum yields information about the 2D velocity distribution f(v {sub parallel}, v {sub perpendicular} {sub to}). Observation from different viewing angles allows consequently a tomographic reconstruction of f(v {sub parallel}, v {sub perpendicular} {sub to}). For this purpose, the FIDA diagnostic at ASDEX Upgrade has been extended from two to five views, and the spectrometer setup was improved to allow a simultaneous measurement of blue and red Doppler shifts. These recently developed diagnostic capabilities are used to study changes in the fast-ion distribution, which are caused by Alfven eigenmodes. Moreover, the further acceleration of fast ions through 2{sup nd} harmonic ICRH is investigated and compared to theoretical predictions.
Alfven Eigenmode And Ion Bernstein Wave Studies For Controlling Fusion Alpha Particles
Franklin, F R
1999-01-01
In magnetic confinement fusion reactor plasmas, the charged fusion products (such as alpha particles in deuterium-tritium plasmas) will be the dominant power source, and by controlling these charged fusion products using wave-particle interactions the reactor performance could be optimized. This thesis studies two candidate waves: Mode- Converted Ion Bernstein Waves (MCIBWs) and Alfvé n Eigenmodes (AEs). Rates of MCIBW-driven losses of alpha-like fast deuterons, previously observed in the Tokamak Fusion Test Reactor (TFTR), are reproduced by a new model so that the wave-particle diffusion coefficient can be deduced. The MCIBW power in TFTR is found to be ∼ 1/3 that needed for collisionless alpha particle control...
New Digital Control System for the JET Alfv'en Eigenmode Active Spectroscopy Diagnostic
Woskov, P. P.; Stillerman, J.; Porkolab, M.; Fasoli, A.; Testa, D.; Galvao, R.; Pires Dos Resis, A.; Pires de Sa, W.; Ruchko, L.; Blanchard, P.; Figueiredo, J.; Dorling, S.; Farthing, J.; Graham, M.; Dowson, S.; Yu, L.; Concezzi, S.
2012-10-01
The state-of-the-art JET Alfv'en active spectroscopy diagnostic with eight internal inductive antennas is being upgraded from a single 5 kW tube amplifier to eight parallel, 10 -- 1000 kHz, 4 kW solid state class D power switching amplifiers. A new digital control system has been designed with arbitrary constant phase controlled frequency sweeps for traveling mode studies, amplifier gain control through a feedback loop referenced to programmed antenna current profiles, and integration with CODAS for synchronization, triggering, gating, and fault tripping. A combination of National Instruments Real Time LabView software and FPGA circuits is used to achieve the multiple control requirements with better than 1 ms response. System specifications and digital-analog design trade offs for sweep rates, response times, frequency resolution, and voltage levels will be presented.
Alfven Eigenmode And Ion Bernstein Wave Studies For Controlling Fusion Alpha Particles
Heeter, R F
1999-01-01
In magnetic confinement fusion reactor plasmas, the charged fusion products (such as alpha particles in deuterium-tritium plasmas) will be the dominant power source, and by controlling these charged fusion products using wave-particle interactions the reactor performance could be optimized. This thesis studies two candidate waves: Mode-Converted Ion Bernstein Waves (MCIBWs) and Alfvén Eigenmodes (AEs). Rates of MCIBW-driven losses of alpha-like fast deuterons, previously observed in the Tokamak Fusion Test Reactor (TFTR), are reproduced by a new model so that the wave-particle diffusion coefficient can be deduced. The MCIBW power in TFTR is found to be ∼ 1/3 that needed for collisionless alpha particle control. A reasonable reactor power scaling is derived. To study AEs, existing magnetic fluctuation probes at the Joint European Torus (JET) have been absolutely calibrated from 30–500 kHz for the first time, allowing fluctuation measurements with &vbm0;dBpol&vbm0;/B0&am...
Energy Technology Data Exchange (ETDEWEB)
Spong, D. A. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 (United States); Bass, E. M. [Department of Physics, University of California, San Diego, California 192093 (United States); Deng, W.; Heidbrink, W. W.; Lin, Z. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Tobias, B. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 085430 (United States); Van Zeeland, M. A. [General Atomics, San Diego, California 92121 (United States); Austin, M. E. [Institute for Fusion Studies, University of Texas, Austin, Texas 78712 (United States); Domier, C. W.; Luhmann, N. C. Jr. [Department of Electrical and Computer Engineering and Department of Applied Science, University of California, Davis, California 95616 (United States)
2012-08-15
A verification and validation study is carried out for a sequence of reversed shear Alfven instability time slices. The mode frequency increases in time as the minimum (q{sub min}) in the safety factor profile decreases. Profiles and equilibria are based upon reconstructions of DIII-D discharge (no. 142111) in which many such frequency up-sweeping modes were observed. Calculations of the frequency and mode structure evolution from two gyrokinetic codes, GTC and GYRO, and a gyro-Landau fluid code TAEFL are compared. The experimental mode structure of the instability was measured using time-resolved two-dimensional electron cyclotron emission imaging. The three models reproduce the frequency upsweep event within {+-}10% of each other, and the average of the code predictions is within {+-}8% of the measurements; growth rates are predicted that are consistent with the observed spectral line widths. The mode structures qualitatively agree with respect to radial location and width, dominant poloidal mode number, ballooning structure, and the up-down asymmetry, with some remaining differences in the details. Such similarities and differences between the predictions of the different models and the experimental results are a valuable part of the verification/validation process and help to guide future development of the modeling efforts.
Nonlinear alfv\\'enic fast particle transport and losses
Schneller, Mirjam; García-Muñoz, Manuel; Brüdgam, Michael; Günter, Sibylle
2012-01-01
Magnetohydrodynamic instabilities like Toroidal Alfv\\'en Eigenmodes or core-localized modes such as Beta Induced Alfv\\'en Eigenmodes and Reversed Shear Alfv\\'en Eigenmodes driven by fast particles can lead to significant redistribution and losses in fusion devices. This is observed in many ASDEX Upgrade discharges. The present work aims to understand the underlying resonance mechanisms, especially in the presence of multiple modes with different frequencies. Resonant mode coupling mechanisms are investigated using the drift kinetic HAGIS code [Pinches 1998]. Simulations were performed for different plasma equilibria, in particular for different q profiles, employing the availability of improved experimental data. A study was carried out, investigating double-resonant mode coupling with respect to various overlapping scenarios. It was found that, depending on the radial mode distance, double-resonance is able to enhance growth rates as well as mode amplitudes significantly. Small radial mode distances, however...
Nonlinear dynamics of beta-induced Alfvén eigenmode driven by energetic particles.
Wang, X; Briguglio, S; Chen, L; Di Troia, C; Fogaccia, G; Vlad, G; Zonca, F
2012-10-01
Nonlinear saturation of a beta-induced Alfvén eigenmode, driven by slowing down energetic particles via transit resonance, is investigated by the nonlinear hybrid magnetohyrodynamic gyrokinetic code. Saturation is characterized by frequency chirping and symmetry breaking between co- and counter-passing particles, which can be understood as the evidence of resonance detuning. The scaling of the saturation amplitude with the growth rate is also demonstrated to be consistent with radial resonance detuning due to the radial nonuniformity and mode structure. PMID:23214643
Toroidal Alfven wave stability in ignited tokamaks
Energy Technology Data Exchange (ETDEWEB)
Cheng, C.Z.; Fu, G.Y.; Van Dam, J.W.
1989-01-01
The effects of fusion-product alpha particles on the stability of global-type shear Alfven waves in an ignited tokamak plasma are investigated in toroidal geometry. Finite toroidicity can lead to stabilization of the global Alfven eigenmodes, but it induces a new global shear Alfven eigenmodes, which is strongly destabilized via transit resonance with alpha particles. 8 refs., 2 figs.
Magneto-HydroDynamic activity and Energetic Particles - Application to Beta Alfven Eigenmodes
Nguyen, Christine
2009-01-01
The goal of magnetic fusion research is to extract the power released by fusion reactions and carried by the product of these reactions, liberated at energies of the order of a few MeV. The feasibility of fusion energy production relies on our ability to confine these energetic particles, while keeping the thermonuclear plasma in safe operating conditions. For that purpose, it is necessary to understand and find ways to control the interaction between energetic particles and the thermonuclear...
Energy Technology Data Exchange (ETDEWEB)
Gorelenkov, N. N.; Berk, H. L.; Fredrickson, E.; Sharapov, S. E.
2007-07-02
New global MHD eigenmode solutions arising in gaps in the low frequency Alfvén -acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfvén-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfvén-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta < 2% as well as in NSTX plasmas at relatively high beta > 20%. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfvén coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.
The Alfven wave spectrum of analytic high-beta tokamak equilibria
International Nuclear Information System (INIS)
This thesis addresses a number of problems regarding the equilibrium and stability of a tokamak plasma under fusion conditions. To get insight into the geometric effects on the behaviour of the most prominent global modes, a spectral study was carried out on a class of analytic, noncircular plasma equilibria. Parallel to this work, extending a previous high-beta energy principle a variational principle is developed for the numerical determination of the Alfven spectrum of a high-beta tokamak with arbitrary cross-section. Based on the Lagrangian formalism, representations were derived for the potential and kinetic energy in terms of arbitrary, non-orthogonal flux coordinates, which can be readily implemented in a numerical programme. The method is then tested by using the analytic equilibrium as input. 85 refs.; 32 figs.; 2 tabs
Shukla, P K
2012-01-01
It is shown that a three-dimensional (3D) modified-kinetic Alfv\\'en waves (m-KAWs) can propagate in the form of Alfv\\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \\ll \\beta \\ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\\beta =4 \\pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unperturbed plasma number density, $k_B$ the Boltzmann constant, $T_e (T_e)$ the electron (ion) temperature, and $B_0$ the strength of the ambient magnetic field. The 3D m-KAW equation admits solutions in the form of a Laguerre-Gauss (LG) Alfv\\'enic vortex beam or Alfv\\'enic tornadoes with plasma density whirls that support the dynamics of Alfv\\'en magnetic flux ropes.
Observation of modes at frequencies near the second Alfven gap in TFTR
International Nuclear Information System (INIS)
Modes have been observed near the frequency of the second Alfven gap during off-axis H-minority heating experiments in the circular cross-section Tokamak Fusion Test Reactor. The observation of these modes is surprising in that the second gap, which is generally opened with ellipticity, is expected to be small, of order (r/R)2. A model is proposed in which the second gap is opened by the fast ion beta, which is shown to be able to introduce mode coupling, much as toroidal effects introduce mode coupling for Toroidal Alfven Eigenmodes (TAE). The modes are seen with and without accompanying TAE mode activity
Shukla, P. K.
2012-01-01
It is shown that a three-dimensional (3D) modified-kinetic Alfv\\'en waves (m-KAWs) can propagate in the form of Alfv\\'enic tornadoes characterized by plasma density whirls or magnetic flux ropes carrying orbital angular momentum (OAM). By using the two fluid model, together with Amp\\`ere's law, we derive the wave equation for a 3D m-KAWs in a magnetoplasma with $m_e/m_i \\ll \\beta \\ll 1$, where $m_e$ $(m_i)$ is the electron (ion) mass, $\\beta =4 \\pi n_0 k_B (T_e + T_i)/B_0^2$, $n_0$ the unpert...
Low-n shear Alfven spectra in axisymmetric toroidal plasmas
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In toroidal plasmas, the toroidal magnetic field is nonuniform over a magnetic surface and causes coupling of different poloidal harmonics. It is shown both analytically and numerically that the toroidicity not only breaks up the shear Alfven continuous spectrum, but also creates new, discrete, toroidicity-induced shear Alfven eigenmodes with frequencies inside the continuum gaps. Potential applications of the low-n toroidicity-induced shear Alfven eigenmodes on plasma heating and instabilities are addressed. 17 refs., 4 figs
Nonlinearly Driven Second Harmonics of Alfven Cascades
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In recent experiments on Alcator C-Mod, measurements of density fluctuations with Phase Contrast Imaging through the plasma core show a second harmonic of the basic Alfven Cascade (AC) signal. The present work describes the perturbation at the second harmonic as a nonlinear sideband produced by the Alfven Cascade eigenmode via quadratic terms in the MHD equations. (author)
Alfven wave heating and stability
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Alfven waves in fusion plasmas play an important role in a number of situations. First, in Alfven Wave Heating (AWH) schemes. Second, both theory and experiment have demonstrated the existence of Global Alfven Eigenmodes (GAEs). GAEs have been observed in different tokamaks (PRETEXT, TCA, TEXTOR, etc.) and, more recently, in a stellarator (Wendelstein 7-AS) where they were shown to become unstable under intense Neutral Beam injection. Third, the existence and possible destabilization by fast ions of Toroidicity induced Alfven Eigenmodes (TAEs) has been evidenced both theoretically and experimentally. This destabilization could hamper the operation of a magnetically confined fusion reactor by setting a limit on the number of fusion alpha particles in the plasma. It is therefore crucial to understand the mechanisms leading to the occurrence of the instability and also those that can stabilize the TAEs by increasing the strength of the damping. The aim is to be able to devise possible ways to avoid the instability of Alfven eigenmodes in a region of parameter space that is compatible with the functioning of a fusion reactor. A global perturbative approach is presented to tackle the problem of the linear stability of TAEs. Our model computes the overall wave particle power transfers to the different species and thus could also be applied to the study of alpha power extraction in the presence of Alfven waves. We indicate also how to go beyond the perturbative approach. (author) 15 figs., 38 refs
Ion Heating by Fast Particle Induced Alfven Turbulence
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A novel mechanism that directly transfers energy from Super-Alfvenic energetic ions to thermal ions in high-beta plasmas is described. The mechanism involves the excitation of compressional Alfvin eigenmodes (CAEs) in the frequency range with omega less than or approximately equal to omega(subscript ci). The broadband turbulence resulting from the large number of excited modes causes stochastic diffusion in velocity space, which transfers wave energy to thermal ions. This effect may be important on the National Spherical Torus Experiment (NSTX), and may scale up to reactor scenarios. This has important implications for low aspect ratio reactor concepts, since it potentially allows for the modification of the ignition criterion
Wang, X; Chen, L; Di Troia, C; Fogaccia, G; Vlad, G; Zonca, F
2010-01-01
Adopting the theoretical framework for the generalized fishbonelike dispersion relation, an extended hybrid magnetohydrodynamics gyrokinetic simulation model has been derived analytically by taking into account both thermal ion compressibility and diamagnetic effects in addition to energetic particle kinetic behaviors. The extended model has been used for implementing an eXtended version of Hybrid Magnetohydrodynamics Gyrokinetic Code (XHMGC) to study thermal ion kinetic effects on Alfv\\'enic modes driven by energetic particles, such as kinetic beta induced Alfv\\'en eigenmodes in tokamak fusion plasmas.
Jo, Young Hyun; Lee, Hae June; Mikhailenko, Vladimir V.; Mikhailenko, Vladimir S.
2016-01-01
It was derived that the drift-Alfven instabilities with the shear flow parallel to the magnetic field have significant difference from the drift-Alfven instabilities of a shearless plasma when the ion temperature is comparable with electron temperature for a finite plasma beta. The velocity shear not only modifies the frequency and the growth rate of the known drift-Alfven instability, which develops due to the inverse electron Landau damping, but also triggers a combined effect of the velocity shear and the inverse ion Landau damping, which manifests the development of the ion kinetic shear-flow-driven drift-Alfven instability. The excited unstable waves have the phase velocities along the magnetic field comparable with the ion thermal velocity, and the growth rate is comparable with the frequency. The development of this instability may be the efficient mechanism of the ion energization in shear flows. The levels of the drift--Alfven turbulence, resulted from the development of both instabilities, are determined from the renormalized nonlinear dispersion equation, which accounts for the nonlinear effect of the scattering of ions by the electromagnetic turbulence. The renormalized quasilinear equation for the ion distribution function, which accounts for the same effect of the scattering of ions by electromagnetic turbulence, is derived and employed for the analysis of the ion viscosity and ions heating, resulted from the interactions of ions with drift-Alfven turbulence. In the same way, the phenomena of the ion cyclotron turbulence and anomalous anisotropic heating of ions by ion cyclotron plasma turbulence has numerous practical applications in physics of the near-Earth space plasmas. Using the methodology of the shearing modes, the kinetic theory of the ion cyclotron turbulence of the plasma with transverse current with strong velocity shear has been developed.
Spectrum of compressional Alfven waves
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The spectrum of compressional Alfven eigenmodes localized in the potential well created by a combination of the variation in plasma density and the wave number k/sub perpendicular to/ = m/r, is obtained, and its importance for ratio frequency current drive is discussed. It is found that modes with small parallel wave numbers and frequencies below the ion cyclotron frequency are attractive for current drive
Kinetic Thermal Ions Effects on Alfvenic Fluctuations in Tokamak Plasmas
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Full text: The early observation of beta induced Alfven eigenmodes (BAE) and a variety of recent experimental observations have attracted attention on studying the low-frequency Alfvenic fluctuations in tokamaks. The generalized fishbone-like dispersion relation theoretical framework has been adopted for extending the hybrid model by taking into account both thermal ion compressibility and diamagnetic effects in addition to energetic particles (EP) kinetic behaviours. The extended model has been used for implementing an eXtended version of HMGC (XHMGC). In general, the new version of HMGC can have two species of kinetic particles. On one hand, one can use XHMGC for investigating thermal ion kinetic effects on Alfvenic modes driven by EP. In this case, EP dynamics contribute in the ideal MHD region; while wave-particle resonances with core-plasma ions are important only in a narrow inertial layer centred about the mode rational surface, where the dynamics of EP can be neglected due to their large perpendicular orbits (compared to the layer width). On the other hand, it may be interesting to use XHMGC as a tool to simulate two coexisting EP species, generated e.g. by both ICRH and NBI heating, in order to study linear excitation of Alfvenic fluctuations and Energetic Particle Modes (EPM), as well as the interplay between the respective nonlinear physics. Results of initial-value simulations show that the observed frequency is always slightly higher than the BAE accumulation point and is the same at different radial positions; consistent with the characteristics of a discrete BAE-SAW eigenmode (termed as kinetic BAE or KBAE); however, no discrete eigenmode is found within the gap when MHD is ideally stable. Meanwhile, preliminary simulations of KBAE/EPM driven by purely circulating EP have also been done. So far, the results show that the mode frequency is higher than either theoretical BAE accumulation point frequency or EP transit frequency, and increases with
International Nuclear Information System (INIS)
Adopting the theoretical framework for the generalized fishbonelike dispersion relation, an extended hybrid magnetohydrodynamics gyrokinetic simulation model has been derived analytically by taking into account both thermal ion compressibility and diamagnetic effects in addition to energetic particle kinetic behaviors. The extended model has been used for implementing an extended version of hybrid magnetohydrodynamics gyrokinetic code (XHMGC) to study thermal ion kinetic effects on Alfvenic modes driven by energetic particles, such as kinetic beta induced Alfven eigenmodes in tokamak fusion plasmas. The XHMGC nonlinear model can be used to address a number of problems, where kinetic treatments of both thermal and supra-thermal plasma components are necessary, as theoretically predicted, or where it is desirable to investigate the phenomena connected with the presence of two supra-thermal particle species with different radial profiles and velocity space distributions.
Anisotropic Alfven-ballooning modes in the Earth's magnetosphere
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We have carried out a theoretical analysis of the stability and parallel structure of coupled shear-Alfven and slow-magnetosonic waves in the Earth's inner magnetosphere including effects of finite anisotropic plasma pressure. Multiscale perturbation analysis of the anisotropic Grad-Shafranov equation yields an approximate self-consistent magnetohydrodynamic (MHD) equilibrium. This MHD equilibrium is used in the numerical solution of a set of eigenmode equations which describe the field line eigenfrequency, linear stability, and parallel eigenmode structure. We call these modes anisotropic Alfven-ballooning modes. The main results are: The field line eigenfrequency can be significantly lowered by finite pressure effects. The parallel mode structure of the transverse wave components is fairly insensitive to changes in the plasma pressure but the compressional magnetic component can become highly peaked near the magnetic equator due to increased pressure, especially when P perpendicular > P parallel. For the isotropic case ballooning instability can occur when the ratio of the plasma pressure to the magnetic pressure, exceeds a critical value βoB ∼ 3.5 at the equator. Compared to the isotropic case the critical beta value is lowered by anisotropy, either due to decreased field-line-bending stabilization when P parallel > P perpendicular, or due to increased ballooning-mirror destabilization when P perpendicular > P parallel. We use a ''β-6 stability diagram'' to display the regions of instability with respect to the equatorial values of the parameters bar β and δ, where bar β = (1/3)(βparallel + 2 β perpendicular) is an average beta value and δ = 1 - P parallel/P perpendicular is a measure of the plasma anisotropy
Shear Alfven waves in tokamaks
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Shear Alfven waves in an axisymmetric tokamak are examined within the framework of the linearized ideal MHD equations. Properties of the shear Alfven continuous spectrum are studied both analytically and numerically. Implications of these results in regards to low frequency rf heating of toroidally confined plasmas are discussed. The structure of the spatial singularities associated with these waves is determined. A reduced set of ideal MHD equations is derived to describe these waves in a very low beta plasma
Cao, G. M.; Li, Y. D.; Li, Q.; Sun, P. J.; Wu, G. J.; Hu, L. Q.; the EAST Team
2015-08-01
Beta-induced Alfvén eigenmodes (BAEs) during strong tearing modes (TMs) have been frequently observed in fast-electron plasmas of EAST tokamak. The dynamics of the short-scale ({k}\\perp {ρ }s~{1.5-4.3}) density fluctuations during the activity of BAEs with strong TMs has been preliminarily investigated by a tangential CO2 laser collective scattering system. The results suggest the active, but different, response of short-scale density fluctuations to the TMs and BAEs. In the low-frequency (0-10 kHz) part of density fluctuations, there are harmonic oscillations totally corresponding to those of TMs. In the medium-high frequency (10-250 kHz) part of density fluctuations, with the appearance of the BAEs, the medium-high frequency density fluctuations begin to be dominated by several quasi-coherent (QC) modes, and the frequencies of the QC modes seem to be related to the changes of both TMs and BAEs. These results would shed some light on the understanding of the multi-scale interaction physics.
Alfven cyclotron instability and ion cyclotron emission
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Two-dimensional solutions of compressional Alfven eigenmodes (CAE) are studied in the cold plasma approximation. For finite inverse aspect ratio tokamak plasmas the two-dimensional eigenmode envelope is localized at the low magnetic field side with the radial and poloidal localization on the order of a/√m and a/(fourth root of m), respectively, where m is the dominant poloidal mode number. Charged fusion product driven Alfven Cyclotron Instability (ACI) of the compressional Alfven eigenmodes provides the explanation for the ion cyclotron emission (ICE) spectrum observed in tokamak experiments. The ACI is excited by fast charged fusion products via Doppler shifted cyclotron wave-particle resonances. The ion cyclotron and electron Landau dampings and fast particle instability drive are calculated perturbatively for deuterium-deuterium (DD) and deuterium-tritium (DT) plasmas. Near the plasma edge at the low field side the velocity distribution function of charged fusion products is localized in both pitch angle and velocity. The poloidal localization of the eigenmode enhances the ACI growth rates by a factor of √m in comparison with the previous results without poloidal envelope. The thermal ion cyclotron damping determines that only modes with eigenfrequencies at multiples of the edge cyclotron frequency of the background ions can be easily excited and form an ICE spectrum similar to the experimental observations. Theoretical understanding is given for the results of TFTR DD and DT experiments with υα0/υA α0/υA > 1
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Seven chapters are included. Chapters 1 and 2 introduce the Alfven wave and describe its linear properties in a homogeneous medium. Chapters 3 and 4 cover the effects of inhomogeneities on these linear properties. Particular emphasis is placed on the appearance of a continuum spectrum and the associated absorption of the Alfven wave which arise due to the inhomogeneity. The explanation of the physical origin of absorption is given using kinetic theory. Chapter 5 is devoted to the associated plasma instabilities. Nonlinear effects discussed in Chapter 6 include quasilinear diffusion, decay, a solitary wave, and a modulational instability. The principles of Alfven wave heating, a design example and present-day experimental results are described in Chapter 7
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This paper discusses experiments on linear high beta helical axis stellarators. Experiments considered are: formation of linear high beta heliac plasma configurations; Alfven wave heating in a straight tube and in a linear high beat stellarator; shifted hardcore heliac studies; a system for measuring the timing of high-current switches in a pulsed high voltage fusion experiment; HBQM general refurbishment; and proposed experiment on excitation of the m = 1 tilt mode in field-reversed configurations
Peculiarities of destabilization of Alfven modes by energetic ions in stellarators
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Alfven Eigenmodes (AE) associated with the breaking of the axial symmetry in stellarators are considered. Specific calculations are carried out for the Helias reactor HSR4/18. An explanation of the temporal evolution of Alfvenic activity observed in experiments on W7-AS is suggested. (author)
Alfven wave cascades in a tokamak
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Experiments designed for generating internal transport barriers in the plasmas of the Joint European Torus [JET, P. H. Rebut et al., Proceedings of the 10th International Conference, Plasma Physics and Controlled Nuclear Fusion, London (International Atomic Energy Agency, Vienna, 1985), Vol. I, p. 11] reveal cascades of Alfven perturbations with predominantly upward frequency sweeping. These experiments are characterized by a hollow plasma current profile, created by lower hybrid heating and current drive before the main heating power phase. The cascades are driven by ions accelerated with ion cyclotron resonance heating (ICRH). Each cascade consists of many modes with different toroidal mode numbers and different frequencies. The toroidal mode numbers vary from n=1 to n=6. The frequency starts from 20 to 90 kHz and increases up to the frequency range of toroidal Alfven eigenmodes. In the framework of ideal magnetohydrodynamics (MHD) model, a close correlation is found between the time evolution of the Alfven cascades and the evolution of the Alfven continuum frequency at the point of zero magnetic shear. This correlation facilitates the study of the time evolution of both the Alfven continuum and the safety factor, q(r), at the point of zero magnetic shear and makes it possible to use Alfven spectroscopy for studying q(r). Modeling shows that the Alfven cascade occurs when the Alfven continuum frequency has a maximum at the zero shear point. Interpretation of the Alfven cascades is given in terms of a novel-type of energetic particle mode localized at the point where q(r) has a minimum. This interpretation explains the key experimental observations: simultaneous generation of many modes, preferred direction of frequency sweeping, and the absence of strong continuum damping
Multiple-gap theory of toroidal Alfven waves with kinetic effects
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The stability of kinetic toroidal Alfven waves with multi-gap coupling is analyzed by using the two-dimensional ballooning transform. An alternate convergence scheme, based on the smallness of the inverse aspect ratio, is devised. The resulting wave functions are oscillatory and do not balloon in contrast to the wave functions of conventional ballooning theory. It is shown that the single-gap theory is a special, weak shear (s → 0) limit of the formalism. Analytical and numerical results for the two fundamental branches, the ideal toroidal Alfven eigenmode (TAE), and the kinetic toroidal Alfven eigenmode (KTAE) are presented and discussed
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This paper discusses induced axial current studies in a hardcore Theta-Pinch; nonaxisymmetric RF heating of a high-Beta plasma column; formation of Axisymmetric hardcore theta pinches with notched hardcore current; and externally driven till made experiments on the high-beta Q machine field reversed configuration
Alfven cyclotron instability and ion cyclotron emission
International Nuclear Information System (INIS)
Two-dimensional solutions of compressional Alfven eigenmodes (CAEs) are studied in the cold plasma approximation. For finite inverse aspect ratio tokamak plasmas the two-dimensional eigenmode envelope is localized at the low magnetic field side with the radial and poloidal localization on the order of a/√m and a/4√m, respectively, where m is the dominant poloidal mode number. Charged fusion product driven Alfven cyclotron instability (ACI) of the compressional Alfven eigenmodes provides the explanation for the ion cyclotron emission (ICE) spectrum observed in tokamak experiments. The ACI is excited by fast charged fusion products via Doppler shifted cyclotron wave-particle resonances. The ion cyclotron and electron Landau damping and fast particle instability drive are calculated perturbatively for deuterium-deuterium (DD) and deuterium-tritium (DT) plasmas. Near the plasma edge at the low field side the velocity distribution function of charged fusion products is localized in both pitch angle and velocity. The poloidal localization of the eigenmode enhances the ACI growth rates by a factor of √m in comparison with the previous results without poloidal envelope. The thermal ion cyclotron damping determines that only modes with eigenfrequencies at multiples of the edge cyclotron frequency of the background ions can be easily excited and form an ICE spectrum similar to the experimental observations. Theoretical understanding is given for the results of TFTR DD and DT experiments with υα0/υA ≅ 1 and JET experiments with υα0/υA > 1. (author). 15 refs, 7 figs
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The first direct observation of the internal structure of driven global Alfven eigenmodes in a tokamak plasma is presented. A carbon dioxide laser scattering/interferometer has been designed, built, and installed on the PRETEXT tokamak. By using this diagnostic system in the interferometer configuration, we have for the first time, thoroughly investigated the resonance conditions required for, and the spatial wave field structure of, driven plasma eigenmodes at frequencies below the ion cyclotron frequency in a confined, high temperature, tokamak plasma
CHROMOSPHERIC EVAPORATION VIA ALFVEN WAVES
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This paper presents a scenario for the chromospheric evaporation during solar flares, which is inspired by the chain of events leading to the formation of auroral arcs and ionospheric evacuation during magnetospheric substorms. The plasma, ejected from high coronal altitudes during a flare reconnection event, accumulates at the tops of coronal loops by braking of the reconnection flow, possibly by fast shock formation. A high-beta layer forms and distorts the magnetic field. Energy contained in magnetic shear stresses is transported as Alfven waves from the loop-top toward the chromosphere. It is shown that under these conditions the Alfven waves carry enough energy to feed the chromospheric evaporation process. The second subject of this investigation is identification of the most effective energy dumping or wave dissipation process. Several processes are being analyzed: ion-neutral collisions, classical and anomalous field-aligned current dissipation, and critical velocity ionization. All of them are being discarded, either because they turn out to be insufficient or imply very unlikely physical properties of the wave modes. It is finally concluded that turbulent fragmentation of the Alfven waves entering the chromosphere can generate the required damping. The basic process would be phase mixing caused by a strongly inhomogeneous distribution of Alfvenic phase speed and laminar flow breakup by Kelvin-Helmholtz (K-H) instability. The filamentary (fibril) structure of the chromosphere thus appears to be essential for the energy conversion, in which the K-H instability is the first step in a chain of processes leading to ion thermalization, electron heating, and neutral particle ionization. Quantitative estimates suggest that a transverse structure with scales not far below 100 km suffices to produce strong wave damping within a few seconds. Nonthermal broadening of some metallic ion lines observed during the pre-impulsive rise phase of a flare might be a residue of
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The physics of Alfven-wave heating is particularly sensitive to the character of the linear mode conversion which occurs at the Alfven resonance layer. Parameter changes can profoundly affect both the location within the plasma and the mechanism for the power absorption. Under optimal conditions the heating power may be absorbed by electron Landau damping and by electron transit-time magnetic pumping in the plasma interior, or by the same processes acting near the resonance layer on the mode-converted kinetic Alfven wave. The method is outlined for computing the coefficients for reflection, transmission and absorption at the resonance layer and some representative results are offered
Confinement relevant Alfven instabilities in Wendelstein 7-AS
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Full text: An important feature of fast-ion-driven Alfven instabilities (AI) observed in W7-AS is that they can result in thermal crashes (the temperature can drop by up to 50%). The purposes of this work are to explain the mentioned phenomenon and develop further the theory of AI in stellarators. Possible mechanisms of the formation of magnetic islands / the stochastization of magnetic field lines are analysed. It is shown that the process affects mainly electrons but not the bulk plasma ions. The behaviour of the Alfven continuum near a point where two gaps cross is studied, and the phenomenon of the gap annihilation at the crossing point is found. The developed theory is applied to the W7-AS shot no. 34723. The Alfven continuum and eigenmodes are calculated. The growth rate of the eigenmodes is determined with taking into account the continuum damping and the collisional damping. The effect of the instability on the thermal plasma is evaluated and compared with experimental results. (author)
Alfven frequency modes at the edge of TFTR plasmas
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An Alfven frequency mode (AFM) is very often seen in TFTR neutral beam heated plasmas as well as ohmic plasmas. This quasi-coherent mode is so far only seen on the magnetic fluctuation diagnostics (Mirnov coils). A close correlation between the plasma edge density and the mode activity (frequency and amplitude) has been observed, which indicates that the AFM is an edge localized mode with r/a > 0.85. No direct impact of this mode on the plasma global performance or fast ion loss (e.g., the α-particles in DT experiments) has been observed. This mode is apparently not the conventional TAE (toroidicity-induced Alfven eigenmodes). The present TAE theory cannot explain the observation. Other possible explanations are discussed
Stability of global Alfven waves (TAE, EAE) in JET tritium discharges
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The study of MHD modes driven unstable by energetic particles due to additional heating and, in particular, by alpha particles is crucial for the prediction of α-confinement for future JET D-T discharges aiming at QDT≅1. In this paper we analyse the toroidicity and elongation induced Alfven eigenmodes (TAE, EAE), their damping and their destabilisation by energetic particles. The spectral code CASTOR (Complex Alfven Spectrum for Toroidal Plasmas) together with the equilibrium solver HELENA provides the tool for the analysis of the ideal and dissipative MHD spectrum. (author) 3 refs., 3 figs
Linear gyrokinetic particle-in-cell simulations of Alfven instabilities in tokamaks
Biancalani, A; Briguglio, S; Koenies, A; Lauber, Ph; Mishchenko, A; Poli, E; Scott, B D; Zonca, F
2015-01-01
The linear dynamics of Alfven modes in tokamaks is investigated here by means of the global gyrokinetic particle-in-cell code NEMORB. The model equations are shown and the local shear Alfven wave dispersion relation is derived, recovering the continuous spectrum in the incompressible ideal MHD limit. A verification and benchmark analysis is performed for continuum modes in a cylinder and for toroidicity-induced Alfven Eigenmodes. Modes in a reversed-shear equilibrium are also investigated, and the dependence of the spatial structure in the poloidal plane on the equilibrium parameters is described. In particular, a phase-shift in the poloidal angle is found to be present for modes whose frequency touches the continuum, whereas a radial symmetry is found to be characteristic of modes in the continuum gap.
Analysis of Alfven Wave Activity in KSTAR Plasmas
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Full text: We report on evidence of neutral beam driven wave activity in KSTAR plasmas. In 2010 and 2011 campaigns KSTAR plasmas included 1MW of neutral beam heating, which provided drive for Alfvenic wave activity modes. Data from the 2010 campaign, which was fully analysed during 2011, identifies the 40 kHz magnetic fluctuations as a β-induced Alfven eignemode resonant with the q = 1 surface. Evidence is multiple fold: a Fourier mode analysis identifies the mode as n = 1. Electron cyclotron emission chords identify the q = 1 inversion radius. These constrain equilibrium reconstruction, and permit detailed MHD calculations using the global MHD stability code MISHKA. A scan of mode frequency near the q = 1 minimum of the continuum identifies a core localised n = 1 mode separated from the continuum. A complementary kinetic analysis, when coupled with ion and electron temperature measurements ratios obtain from crystallography, enables calculation of the frequency evolution - which is in agreement with observations. In 2011 a series of experiments were conducted to scope Alfven excitation using NBI and ECRH heating as a function of field strength and plasma current. In these experiments plasmas with toroidal current up to 600 kA were generated with 1.5 MW of NBI heating and up to 120 kW of co or counter ECRH, and the field strength varied from 1.7 T to 2 T. Spectral and mode number analysis of the magnetics data identifies 150 - 250 kHz coherent activity with a toroidal mode number of n = 1. Assuming a poloidal mode number of m = 1, we have computed the evolution of the toroidal Alfven eigenmode (TAE) middle of the gap frequency, and compared the frequency evolution to magnetic spectrograms. While the frequency of the mode is above the Nyquist frequency, the aliased frequency tracks the observations to within 20%, providing some confidence of a TAE interpretation. Finally, we also report evidence of ion fishbone activity. (author)
Institute of Scientific and Technical Information of China (English)
K. OGAWA; M. ISOBE; K. TOI; F. WATANABE; D. A. SPONG; A. SHIMIZU; M. OSAKABE; D. S. DARROW; S. OHDACHI; S. SAKAKIBARA; LHD Experiment -Group
2012-01-01
Beam-ion losses induced by fast-ion-driven toroidal Alfven eigenmodes （TAE） were measured with a scintillator-based lost fast-ion probe （SLIP） in the large helical device （LHD）. The SLIP gave simultaneously the energy E and the pitch angle X=arccos（v///v） distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of Rax-vac=3.60 m, 3.75 m. and 3.90 m, where Rax-vac is the magnetic axis position of the vacuum field. Dominant losses induced by TAEs in these three configurations were observed in the E/X regions of 50-190 keV/40°, 40-170 keV/25°, and 30-190 keV/30°, respectively. Lost-ion fluxes induced by TAEs depend clearly on the amplitude of TAE magnetic fluctuations, Rax-vac and the toroidal field strength Bt. The increment of the loss fluxes has the dependence of （bTAE/Bt）s. The power s increases from s = 1 to 3 with the increase of the magnetic axis position in finite beta plasmas.
Energy Technology Data Exchange (ETDEWEB)
Weng, C. J. [Department of Physics, National Cheng Kung University, Tainan 701, Taiwan (China); Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Lee, L. C. [Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Institute of Earth Science, Academia Sinica, Nankang 115, Taiwan (China); Kuo, C. L. [Institute of Space Science, National Central University, Jhongli 320, Taiwan (China); Wang, C. B. [CAS Key Laboratory of Geospace Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei (China)
2013-03-15
Alfven waves are low-frequency transverse waves propagating in a magnetized plasma. We define the Alfven frequency {omega}{sub 0} as {omega}{sub 0}=kV{sub A}cos{theta}, where k is the wave number, V{sub A} is the Alfven speed, and {theta} is the angle between the wave vector and the ambient magnetic field. There are partially ionized plasmas in laboratory, space, and astrophysical plasma systems, such as in the solar chromosphere, interstellar clouds, and the earth ionosphere. The presence of neutral particles may modify the wave frequency and cause damping of Alfven waves. The effects on Alfven waves depend on two parameters: (1) {alpha}=n{sub n}/n{sub i}, the ratio of neutral density (n{sub n}), and ion density (n{sub i}); (2) {beta}={nu}{sub ni}/{omega}{sub 0}, the ratio of neutral collisional frequency by ions {nu}{sub ni} to the Alfven frequency {omega}{sub 0}. Most of the previous studies examined only the limiting case with a relatively large neutral collisional frequency or {beta} Much-Greater-Than 1. In the present paper, the dispersion relation for Alfven waves is solved for all values of {alpha} and {beta}. Approximate solutions in the limit {beta} Much-Greater-Than 1 as well as {beta} Much-Less-Than 1 are obtained. It is found for the first time that there is a 'forbidden zone (FZ)' in the {alpha}-{beta} parameter space, where the real frequency of Alfven waves becomes zero. We also solve the wavenumber k from the dispersion equation for a fixed frequency and find the existence of a 'heavy damping zone (HDZ).' We then examine the presence of FZ and HDZ for Alfven waves in the ionosphere and in the solar chromosphere.
The effect of compressibility on the Alfven spatial resonance heating
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The effect of compressibility of magnetic field line on the damping rate of Alfven spatial resonance heating for a high beta plasma (Kinetic pressure/magnetic pressure) was analysed, using the ideal MHD (Magnetohydrodynamic) model in cylindrical geometry for a diffuse θ-pinch with conducting wall. The dispersion relation was obtained solving the equation of motion in the plasma and vacuum regions together with boundary conditions. (Author)
Simulation of the interaction between Alfven waves and fast particles
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There is a wide variety of Alfven waves in tokamak and stellarator plasmas. While most of them are damped, some of the global eigenmodes can be driven unstable when they interact with energetic particles. By coupling the MHD code CKA with the gyrokinetic code EUTERPE, a hybrid kinetic-MHD model is created to describe this wave-particle interaction in stellarator geometry. In this thesis, the CKA-EUTERPE code package is presented. This numerical tool can be used for linear perturbative stability analysis of Alfven waves in the presence of energetic particles. The equations for the hybrid model are based on the gyrokinetic equations. The fast particles are described with linearized gyrokinetic equations. The reduced MHD equations are derived by taking velocity moments of the gyrokinetic equations. An equation for describing the Alfven waves is derived by combining the reduced MHD equations. The Alfven wave equation can retain kinetic corrections. Considering the energy transfer between the particles and the waves, the stability of the waves can be calculated. Numerically, the Alfven waves are calculated using the CKA code. The equations are solved as an eigenvalue problem to determine the frequency spectrum and the mode structure of the waves. The results of the MHD model are in good agreement with other sophisticated MHD codes. CKA results are shown for a JET and a W7-AS example. The linear version of the EUTERPE code is used to study the motion of energetic particles in the wavefield with fixed spatial structure, and harmonic oscillations in time. In EUTERPE, the gyrokinetic equations are discretized with a PIC scheme using the delta-f method, and both full orbit width and finite Larmor radius effects are included. The code is modified to be able to use the wavefield calculated externally by CKA. Different slowing-down distribution functions are also implemented. The work done by the electric field on the particles is measured to calculate the energy transfer
Alfven solitons in the solar wind
Ovenden, C.; Schwartz, S. J.
1983-01-01
A nonlinear Alfven soliton solution of the MHD equations is presented. This solution represents the final state of modulationally unstable Alfven waves. A model of the expected turbulent spectrum due to a collection of such solitons is briefly described.
International Nuclear Information System (INIS)
Kinetic effects of Alfven wave spatial resonances near the plasma edge are investigated numerically and analytically in a cylindrical tokamak model. In Part 1, cold plasma surface Alfven eigenmodes (SAE's) in a pure plasma are examined. Numerical calculations of antenna-driven waves exhibiting absorption resonances at certain discrete frequencies are first reviewed. From a simplified kinetic equation, an analytical dispersion relation is then obtained with the antenna current set equal to zero. The real and imaginary parts of its roots, which are the complex eigenfrequencies, agree with the central frequencies and widths, respectively, of the numerical antenna-driven resonances. These results serve as an introduction to the companion paper, in which it is shown that, in the presence of a minority species, certain SAE's, instead of heating the plasma exterior, can dissipate substantial energy in the two-ion hybrid layer near the plasma center. 11 refs., 8 figs., 1 tab
Streaming tearing instability in the current sheet with a super-Alfvenic flow
International Nuclear Information System (INIS)
The tearing instability in a current sheet, which has a sub-Alfvenic or super-Alfvenic plasma flow in the current layer, is investigated based on the linearized compressible magnetohydrodynamic (MHD) equations. An initial-value method is employed to obtain the linear growth rate and eigenmode profiles of the fastest growing mode. The results show that for a sub-Alfvenic plasma flow parallel to the neutral sheet, the growth rate of the tearing instability is only slightly larger than that of the pure tearing mode without the flow. On the other hand, a large increase in the growth rate of the most unstable mode is observed, when the streaming speed V0/sub m/ in the central region of the current sheet increases above a critical speed V/sub C/≅1.2V/sub A//sub ∞/. Here V/sub A//sub ∞/ is the Alfven speed far away from the current layer. This study shows that when the electric resistivity eta is zero, the sausage mode is excited because of a super-Alfvenic plasma flow parallel to the current sheet. This flow-induced sausage mode is called the streaming sausage mode. In the presence of a finite resistivity, the streaming sausage mode becomes a mixed sausage--tearing mode, because of the presence of magnetic field line reconnections in the current sheet. This mixed sausage--tearing mode, or simply the streaming tearing mode, has a high growth rate, γ≅0.1tau-1/sub A/, where tau/sub A/ is the Alfven transit time across the current layer
Formation of quasiparallel Alfven solitons
Hamilton, R. L.; Kennel, C. F.; Mjolhus, E.
1992-01-01
The formation of quasi-parallel Alfven solitons is investigated through the inverse scattering transformation (IST) for the derivative nonlinear Schroedinger (DNLS) equation. The DNLS has a rich complement of soliton solutions consisting of a two-parameter soliton family and a one-parameter bright/dark soliton family. In this paper, the physical roles and origins of these soliton families are inferred through an analytic study of the scattering data generated by the IST for a set of initial profiles. The DNLS equation has as limiting forms the nonlinear Schroedinger (NLS), Korteweg-de-Vries (KdV) and modified Korteweg-de-Vries (MKdV) equations. Each of these limits is briefly reviewed in the physical context of quasi-parallel Alfven waves. The existence of these limiting forms serves as a natural framework for discussing the formation of Alfven solitons.
Three-dimensional computation of drift Alfven turbulence
International Nuclear Information System (INIS)
A transcollisional, electromagnetic fluid model, incorporating the parallel heat flux as a dependent variable, is constructed to treat electron drift turbulence in the regime of tokamak edge plasma at the L-H transition. The resulting turbulence is very sensitive to the plasma beta throughout this regime, with the scaling with rising beta produced by the effect of magnetic induction to slow the Alfvenic parallel electron dynamics and thereby leave the turbulence in a more robust, non-adiabatic state. Magnetic flutter and curvature have a minor quantitative effect is strong. Transport by magnetic flutter is small compared to that by the E x B flow eddies. Fluctuation statistics show that while the turbulence shows no coherent structure, it is coupled strongly enough so that neither density nor temperature fluctuations behave as passive scalars. Both profile gradients drive the turbulence, with the total thermal energy transport varying only weakly with the gradient ratio, d log T/d log n. Scaling with magnetic shear is pronounced, with stronger shear leading to lower drive levels. Scaling with either collision frequency or magnetic curvature is weak, consistent with their weak qualitative effect. The result is that electron drift turbulence at L-H transition edge parameters is drift Alfven turbulence, with both ballooning and resistivity in a clear secondary role. The contents of the drift Alfven model will form a significant part of any useful first-principles computation of tokamak edge turbulence. (Author)
One-dimensional model of global Alfven Eigenmodes in TORTUS and Wendelstein WVII-AS
International Nuclear Information System (INIS)
In this article, a model for GAEs in a screw pinch plasma geometry is presented. The wave equations are derived from an ideal MHD model with corrections for finite frequency. Analytical and numerical solutions of these equations, applied to parameter sets approximating the TORTUS Tokamak and the Wendelstein WVII-AS advanced stellarator, are presented and discussed. (orig.)
James Clerk Maxwell Prize for Plasma Physics Talk: On Nonlinear Physics of Shear Alfv'en Waves
Chen, Liu
2012-10-01
Shear Alfv'en Waves (SAW) are electromagnetic oscillations prevalent in laboratory and nature magnetized plasmas. Due to its anisotropic propagation property, it is well known that the linear wave propagation and dispersiveness of SAW are fundamentally affected by plasma nonuniformities and magnetic field geometries; for example, the existence of continuous spectrum, spectral gaps, and discrete eigenmodes in toroidal plasmas. This talk will discuss the crucial roles that nonuniformity and geometry could also play in the physics of nonlinear SAW interactions. More specifically, the focus will be on the Alfv'enic state and its breaking up by finite compressibility, non-ideal kinetic effects, and geometry. In the case of compressibility, finite ion-Larmor-radius effects are shown to qualitatively and quantitatively modify the three-wave parametric decays via the ion-sound perturbations. In the case of geometry, the spontaneous excitation of zonal structures by toroidal Alfv'en eigenmodes is investigated; demonstrating that, for realistic tokamak geometries, zonal current dominates over zonal flow. [4pt] Present address: Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China.
Rogue waves in Alfvenic turbulence
International Nuclear Information System (INIS)
Rogue waves, in the form of giant breathers, are shown to develop in the Alfven wave (AW) turbulence regime described by the randomly driven derivative nonlinear Schroedinger equation in the presence of a weak dissipation. The distribution of the instantaneous global maxima of the AW intensity fluctuations is seen to be accurately fitted by power laws, which contrasts with the integrable regime (absence of dissipation and forcing) where the behavior is rather exponential. As the dissipation is reduced, freak waves form less frequently but reach larger amplitudes. -- Highlights: → Rogue wave formation in long-wavelength Alfvenic turbulence. → Huge waves form by quasi-collapse of breathers in presence of weak dissipation. → Amplitude distribution of rogue waves is fitted by power laws. → Possible relation with SLAMS pulses observed near the Earth bow shock.
Finite amplitude solitary Alfven waves in a low-β plasma
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Different exact forms of Alfven solitons were found recently in low-beta plasmas by different assumptions. The present paper studies the case of parallel ion inertia and current density. Both super and sub-Alfvenian rarefactive solitons were found to exist depending on the angle of inclination of the propagation vector with the magnetic field. (D.Gy.)
Experimental studies of Alfven mode stability in the JET tokamak
International Nuclear Information System (INIS)
Controlling the interaction between fusion generated α's and modes in the Alfven frequency range is a crucial issue for the operation of experimental reactors in the burning plasma regime, such as ITER, as these modes can be driven unstable by the slowing-down α's up to amplitudes at which they could cause rapid radial transport of the α's themselves. The need to avoid strongly unstable regimes for some classes of Alfven Eigenmodes (AEs) could therefore provide additional operational limits for the reactor regime. On the other hand, if adequate actuators are identified, AEs could be used to affect the thermonuclear plasma burn in a controlled way. Two classes of investigations are conducted on JET to directly observe the AE stability limits in the presence of fast particles that can resonate with the modes and to measure the damping rate of the modes as a function of the plasma parameters, in order to quantify the mechanisms that provide background damping for the modes in different conditions. Sections 2 and 3 describe experiments from the first class, addressing the AE stability threshold for different fast ion radial distributions, generated at different locations by additional heating or at different plasma densities, or modified by the presence of error field mode. Examples from the second class are described in Section 4. During the last two years a particular effort was undertaken to complete the database of damping rate measurements of low toroidal mode numbers using the saddle coil active AE excitation system, which is being dismantled during the 2004 JET shutdown. A new antenna system is under development to continue along the same lines, but extending the accessible range of toroidal mode numbers to higher values, up to n >>10-15, of more direct relevance to ITER. This system is described in Section 5
Characteristics of Short-wavelength Oblique Alfven and Slow waves
Zhao, J S; Yu, M Y; Lu, J Y; Wu, D J
2014-01-01
Linear properties of kinetic Alfv\\'en waves (KAWs) and kinetic slow waves (KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We obtain the wave dispersion relations that are valid in a wide range of the wave frequency {\\omega} and plasma-to-magnetic pressure ratio {\\beta}. The KAW frequency can reach and exceed the ion cyclotron frequency at ion kinetic scales, whereas the KSW frequency remains sub-cyclotron. At {\\beta}\\sim1, the plasma and magnetic pressure perturbations of both modes are in anti-phase, so that there is nearly no total pressure perturbations. However, these modes exhibit several different properties. At high {\\beta}, the electric field polarization of KAW and KSW is opposite at the ion gyroradius scale, where KAWs are polarized in sense of electron gyration (right-hand polarized) and KSWs are left-hand polarized. The magnetic helicity {\\sigma}\\sim1 for KAWs and {\\sigma}\\sim-1 for KSWs, and the ion Alfv\\'en ratio R_{Ai}\\ll 1 for KAWs and R_{Ai}\\gg 1 for KSWs. We also found...
Polyakov loop fluctuations in Dirac eigenmode expansion
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-01-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal non-twisted periodic boundary condition for the link-variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phase by numerical simulations in SU(3) quenched QCD. Thes...
International Nuclear Information System (INIS)
Alfven instabilities driven by fast ions have been observed in many experiments on tokamaks and stellarators. In tokamaks, they can strongly affect the fast ion confinement but not the bulk plasma. In contrast to this, experiments on the Wendelstein 7-AS (W7-AS) stellarator have shown that Alfvenic activity can strongly deteriorate the global energy confinement time: strong thermal crashes (the temperature dropped by up to 30%) were reported in Ref. [1] and observed also in the last series of experiments in 2002. To explain this phenomenon, recently a new mechanism of anomalous electron heat conductivity associated with Kinetic Alfven Waves (KAW) was suggested. In this work, we further develop theory required for the interpretation of experimental observations of Alfvenic activity in W7-AS and analyse a particular shot (No. 34723) where strong drops of the plasma energy content took place in details. As a result, (i) we identified the instability observed in the mentioned W7-AS shot as Non- conventional Global Alfven Eigenmode (NGAE), (ii) suggested an explanation of the frequency chirping (from ∼70 kHz to ∼45 kHz) during the instability bursts, (iii) showed why the instability was most strong at the end of the bursts when thermal crashes occurred, (iv) considered two possible mechanisms of thermal crashes (anomalous heat conductivity and instability-induced-loss of the injected ions), (v) made a modelling of oscillations of the plasma energy content. An important role of the finite orbit width of fast ions was revealed: it was found that finite orbits actually trigger the instability at ω≤ 70 kHz and weaken the mode destabilization at the end of the instability bursts (when ω≥ 40 kHz). It was concluded that the observed frequency chirping can be explained by the expulsion of fast ions from the plasma core and a concomitant local change of the rotational transform. In order to identify the instability, the Alfven continuum and Alfven eigenmodes were
Three-dimensional numerical simulations of fast-to-Alfven conversion in sunspots
Felipe, T
2012-01-01
The conversion of fast waves to the Alfven mode in a realistic sunspot atmosphere is studied through three-dimensional numerical simulations. An upward propagating fast acoustic wave is excited in the high-beta region of the model. The new wave modes generated at the conversion layer are analyzed from the projections of the velocity and magnetic field in their characteristic directions, and the computation of their wave energy and fluxes. The analysis reveals that the maximum efficiency of the conversion to the slow mode is obtained for inclinations of 25 degrees and low azimuths, while the Alfven wave conversions peaks at high inclinations and azimuths between 50 and 120 degrees. Downward propagating Alfven waves appear at the regions of the sunspot where the orientation of the magnetic field is in the direction opposite to the wave propagation, since at these locations the Alfven wave couples better with the downgoing fast magnetic wave which are reflected due to the gradients of the Alfven speed. The simul...
MIMO Identical Eigenmode Transmission System (IETS) - a Channel Decomposition Perspective
Shakir, Muhammad Zeeshan; Durrani, Tariq
2007-01-01
In the past few years considerable attention has been given to the design of Multiple-Input Multiple-Output (MIMO) Eigenmode Transmission Systems (EMTS). This paper presents an in-depth analysis of a new MIMO eigenmode transmission strategy. The non-linear decomposition technique called Geometric Mean Decomposition (GMD) is employed for the formation of eigenmodes over MIMO flatfading channel. Exploiting GMD technique, identical, parallel and independent transmission pipes are created for dat...
Alfven Wave Tomography for Cold MHD Plasmas
International Nuclear Information System (INIS)
Alfven waves propagation in slightly nonuniform cold plasmas is studied by means of ideal magnetohydrodynamics (MHD) nonlinear equations. The evolution of the MHD spectrum is shown to be governed by a matrix linear differential equation with constant coefficients determined by the spectrum of quasi-static plasma density perturbations. The Alfven waves are shown not to affect the plasma density inhomogeneities, as they scatter off of them. The application of the MHD spectrum evolution equation to the inverse scattering problem allows tomographic measurements of the plasma density profile by scanning the plasma volume with Alfven radiation
Interchange Reconnection Alfven Wave Generation
Lynch, B J; Li, Y
2014-01-01
Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfven waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly-open field lines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high frequency component associated with the current sheet/reconnection site and an extended low frequency component associ...
Spheromak heating with Alfven waves
International Nuclear Information System (INIS)
The temperature of present spheromak plasmas will need to be raised in order to test the feasibility of the confinement concept. In addition, a spatially-selective rf heating pulse can be used to study transport. As the ohmic heating power within a spheromak can be quite large (6-MW), low frequencies where large amounts of power are available are preferred. For the Los Alamos spheromak experiment CTX, we propose to add heating energy via a shear Alfven wave resonance. This resonance can be made to occur upon a particular flux surface, thus depositing most of the energy locally. A 2-dimensional equilibrium code (toroidally symmetric) is used to establish flux surfaces and magnetic field values for the desired configuration, either with or without plasma pressure
Polyakov loop fluctuations in Dirac eigenmode expansion
Doi, Takahiro M; Sasaki, Chihiro; Suganuma, Hideo
2015-01-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal non-twisted periodic boundary condition for the link-variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phase by numerical simulations in quenched QCD. These results indicate that there is no direct, one-to-one correspondence between confinement and chiral symmetry breaking in QCD in the context of different properties of the Polyakov loop fluctuation ratios.
The Eigenmode Analysis of Human Motion
Park, Juyong; Gonzalez, Marta C
2016-01-01
Rapid advances in modern communication technology are enabling the accumulation of large-scale, high-resolution observational data of spatiotemporal movements of humans. Classification and prediction of human mobility based on the analysis of such data carry great potential in applications such as urban planning as well as being of theoretical interest. A robust theoretical framework is therefore required to study and properly understand human motion. Here we perform the eigenmode analysis of human motion data gathered from mobile communication records, which allows us to explore the scaling properties and characteristics of human motion.
Continuum Eigenmodes in Some Linear Stellar Models
Winfield, Christopher J
2016-01-01
We apply parallel approaches in the study of continuous spectra to adiabatic stellar models. We seek continuum eigenmodes for the LAWE formulated as both finite difference and linear differential equations. In particular, we apply methods of Jacobi matrices and methods of subordinancy theory in these respective formulations. We find certain pressure-density conditions which admit positive-measured sets of continuous oscillation spectra under plausible conditions on density and pressure. We arrive at results of unbounded oscillations and computational or, perhaps, dynamic instability.
The eigenmode analysis of human motion
International Nuclear Information System (INIS)
Rapid advances in modern communication technology are enabling the accumulation of large-scale, high-resolution observational data of the spatiotemporal movements of humans. Classification and prediction of human mobility based on the analysis of such data has great potential in applications such as urban planning in addition to being a subject of theoretical interest. A robust theoretical framework is therefore required to study and properly understand human motion. Here we perform the eigenmode analysis of human motion data gathered from mobile communication records, which allows us to explore the scaling properties and characteristics of human motion
Alfven wave. DOE Critical Review Series
International Nuclear Information System (INIS)
This monograph deals with the properties of Alfven waves and with their application to fusion. The book is divided into 7 chapters dealing with linear properties in homogeneous and inhomogeneous plasmas. Absorption is treated by means of kinetic theory. Instabilities and nonlinear processes are treated in Chapters 1 to 6, and the closing chapter is devoted to theory and experiments in plasma heating by Alfven waves
Alfven wave. DOE Critical Review Series
Energy Technology Data Exchange (ETDEWEB)
Hasegawa, A.; Uberoi, C.
1982-01-01
This monograph deals with the properties of Alfven waves and with their application to fusion. The book is divided into 7 chapters dealing with linear properties in homogeneous and inhomogeneous plasmas. Absorption is treated by means of kinetic theory. Instabilities and nonlinear processes are treated in Chapters 1 to 6, and the closing chapter is devoted to theory and experiments in plasma heating by Alfven waves. (MOW)
Nonlinear Energetic Particle Transport in the Presence of Multiple Alfvenic Waves in ITER
Schneller, Mirjam; Briguglio, Sergio
2015-01-01
This work presents the results of a multi mode ITER study on Toroidal Alfven Eigenmodes, using the nonlinear hybrid HAGIS-LIGKA model. It is found that main conclusions from earlier studies of ASDEX Upgrade discharges can be transferred to the ITER scenario: global, nonlinear effects are crucial for the evolution of the multi mode scenario. This work focuses on the ITER 15 MA baseline scenario with with a safety factor at the magnetic axis of $q_0 =$ 0.986. The least damped eigenmodes of the system are identified with the gyrokinetic, non-perturbative LIGKA solver, concerning mode structure, frequency and damping. Taking into account all weakly damped modes that can be identified linearly, nonlinear simulations with HAGIS reveal strong multi mode behavior: while in some parameter range, quasi-linear estimates turn out to be reasonable approximations for the nonlinearly relaxed energetic particle profile, under certain conditions low-n TAE branches can be excited. As a consequence, not only grow amplitudes of ...
Effect of Rossby and Alfv\\'{e}n waves on the dynamics of the tachocline
Leprovost, Nicolas; Kim, Eun-Jin
2006-01-01
To understand magnetic diffusion, momentum transport, and mixing in the interior of the sun, we consider an idealized model of the tachocline, namely magnetohydrodynamics (MHD) turbulence on a $\\beta$ plane subject to a large scale shear (provided by the latitudinal differential rotation). This model enables us to self-consistently derive the influence of shear, Rossby and Alfv\\'{e}n waves on the transport properties of turbulence. In the strong magnetic field regime, we find that the turbule...
Alfvenic waves in solar spicules
Ebadi, Hossein
2016-07-01
We analyzed O VI (1031.93 A) and O VI (1037.61 A line profiles from the time series of SOHO/SUMER data. The wavelet analysis is used to determine the fundamental mode and its first harmonic periods and their ratio. The period ratio, P_1/P_2 is obtained as 2.1 based on our calculations. To model the spicule oscillations, we consider an equilibrium configuration in the form of an expanding straight magnetic flux tube with varying density along tube. We used cylindrical coordinates r, phi, and z with the z-axis along tube axis. Standing Alfvenic waves with steady flows are studied. More realistic background magnetic field, plasma density, and spicule radios inferred from the actual magnetoseismology of observations are used. It is found that the oscillation periods and their ratio are shifted because of the steady flows. The observational values are reached in P_1/P_2, when the steady flows are 0.2-0.3, the values which are reported for classical spicules.
Influence of radial electric field on Alfven-type instabilities
Energy Technology Data Exchange (ETDEWEB)
Hahm, T.S.; Tang, W.M.
1994-03-01
The influence of the large scale radial electric field, E{sub r}{sup (0)} on the frequency of shear-Alfven-type instability is analyzed. A frozen-in-flux constraint and the moderate-{beta} ion gyrokinetic equation are used in the derivation. The analysis indicates that the frequency predicted by a theory with E{sub r}{sup (0)} effect should be Doppler-shifted by k {center_dot} V{sub E} for comparison to the experimentally observed frequency. A specific example of the practical relevance of the result is given regarding possible identification of the edge-localized-mode-associated magnetic activity recently observed in PBX-M tokamak experiment.
Neugebauer, M.; Buti, B.
1990-01-01
Results are presented of a study designed to confirm the suspected relation between Alfven solitons (steepened Afven waves) and rotational discontinuities (RDs) in the solar wind. The ISEE 3 data were used to search for the predicted correlations between the beta value of plasma, the sense of polarization of the discontinuity, and changes of the magnetic field strength and plasma density across the discontinuity. No statistically significant evidence was found for the evolution of RDs from Alfven solitons. A possibility is suggested that the observations made could have been far from the regions in which the RDs were formed.
Roles of Fast-Cyclotron and Alfven-Cyclotron Waves for the Multi-Ion Solar Wind
Xiong, Ming; Li, Xing
2012-01-01
Using linear Vlasov theory of plasma waves and quasi-linear theory of resonant wave-particle interaction, the dispersion relations and the electromagnetic field fluctuations of fast and Alfven waves are studied for a low-beta multi-ion plasma in the inner corona. Their probable roles in heating and accelerating the solar wind via Landau and cyclotron resonances are quantified. We assume that (1) low-frequency Alfven and fast waves have the same spectral shape and the same amplitude of power s...
Plasma heating by kinetic Alfven wave
International Nuclear Information System (INIS)
The heating of a nonuniform plasma (electron-ion) due to the resonant excitation of the shear Alfven wave in the low β regime is studied using initially the ideal MHD model and posteriorly using the kinetic model. The Vlasov equation for ions and the drift kinetic equation for electrons have been used. Through the ideal MHD model, it is concluded that the energy absorption is due to the continuous spectrum (phase mixing) which the shear Alfven wave has in a nonuniform plasma. An explicit expression for the energy absorption is derived. Through the kinetic model it is concluded that the energy absorption is due to a resonant mode convertion of the incident wave into the kinetic Alfven wave which propagates away from the resonant region. Its electron Landau damping has been observed. There has been a concordance with the MHD calculations. (Author)
Alfven wave heating of a theta pinch
International Nuclear Information System (INIS)
The process of shear Alfven wave resonant absorption for plasma heating has been applied to a theta pinch. The m=1 mode is excited by means of a helical launching structure with a given wavelength, at a number of different frequencies. When the frequency lies in the continuous Alfven spectrum the kink energy is transferred to the Alfven wave and then is rapidly thermalized. The heating power is measured by a diamagnetic probe. It is shown that the probe signal can be treated as a thermodynamic variable permitting an exact energy balance to be deduced. The measured resonance curve of the heating power is in agreement with the predicted behaviour. A 50% efficiency is achieved and the coupling between the plasma and the external circuit is strong, in spite of the high compression ratio. (author)
Alfvenic Heating of Protostellar Accretion Disks
Vasconcelos, M. J.; Jatenco-Pereira, V.; R. Opher
1999-01-01
We investigate the effects of heating generated by damping of Alfven waves on protostellar accretion disks. Two mechanisms of damping are investigated, nonlinear and turbulent, which were previously studied in stellar winds (Jatenco-Pereira & Opher 1989a, b). For the nominal values studied, f=delta v/v_{A}=0.002 and F=varpi/Omega_{i}=0.1, where delta v, v_{A} and varpi are the amplitude, velocity and average frequency of the Alfven wave, respectively, and Omega_{i} is the ion cyclotron freque...
Current generation by the Kinetic Alfven wave
International Nuclear Information System (INIS)
The current generated and the efficiency of the shear Kinetic Alfven wave are obtained using a self-consistent quasilinear formulation. Also, the current generation by the monochromatic shear Kinetic Alfven wave introduced by Hasegawa is re-examined taking into account the nonresonant electrons. To obtain the RF current density at the level of the ohmic heating current density in a tokamak, the required external magnetic field is smaller than 0.1% of the DC magnetic field, and the parallel electric field (E2), using the Lausanne-TCA-Tokamak parameters is of the order of 0.01 V cm-1. (author)
On Alfven waves in the solar breeze
International Nuclear Information System (INIS)
The application to the solar wind motivates the consideration of Alfven waves in a radial background magnetic field and radial mean flow, in two cases, viz., with velocity and magnetic field perturbations along parallels, or also with perturbations along meridians, combined in the radial components of vorticity and electric current. In both cases the same second-order Alfven wave equation is obtained; it has, in general, two singularities. If the mean flow velocity is taken to be a power of radial distance, with exponent other than zero or unity, there is a transition layer. In general there is a second singularity, viz., a critical layer, where the Alfven speed equals the mean flow velocity. There is one exceptional case in which the critical layer does not exist, namely a homogeneous medium, for which the mean flow velocity decays on the inverse square of the radial distance, and then Alfven speed also decays in the same way, so that their ratio is a constant, leading to two possibilities: (i) the ratio is not unity, and the wave equation remains of the second-order; (ii) the wave equation becomes of first-order in the case the mean flow velocity and Alfven speed are equal everywhere, because then the waves can propagate only in one direction. Case (i) corresponds to Alfven waves in the solar breeze. Exact solutions of the wave equations are obtained for all values of the radius, as a single expression for the first-order wave equation, whereas for the second-order wave equation it is possible to obtain solutions for small and large radius; the transition level limits the radius of convergence of one of these solutions, but the two solutions together cover the full range of radial distances. The choices of boundary conditions are discussed and the wavefields plotted vs dimensionless distance for several values of the two dimensionless parameters of the problem, viz., the Alfven number and dimensionless frequency, which appear in one combination only. The
Modulational instability of finite-amplitude, circularly polarized Alfven waves
Derby, N. F., Jr.
1978-01-01
The simple theory of the decay instability of Alfven waves is strictly applicable only to a small-amplitude parent wave in a low-beta plasma, but, if the parent wave is circularly polarized, it is possible to analyze the situation without either of these restrictions. Results show that a large-amplitude circularly polarized wave is unstable with respect to decay into three waves, one longitudinal and one transverse wave propagating parallel to the parent wave and one transverse wave propagating antiparallel. The transverse decay products appear at frequencies which are the sum and difference of the frequencies of the parent wave and the longitudinal wave. The decay products are not familiar MHD modes except in the limit of small beta and small amplitude of the parent wave, in which case the decay products are a forward-propagating sound wave and a backward-propagating circularly polarized wave. In this limit the other transverse wave disappears. The effect of finite beta is to reduce the linear growth rate of the instability from the value suggested by the simple theory. Possible applications of these results to the theory of the solar wind are briefly touched upon.
Eigenmodes of three-dimensional magnetic arcades in the Sun's corona
Jain, Bradley W Hindman Rekha
2015-01-01
We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger 3-D magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3-D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3-D waveguide if the Alfv\\'en speed increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1-D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade posse...
Effects of small wavenumber Alfven waves on particle acceleration
International Nuclear Information System (INIS)
Energetic charged particles are accelerated by turbulent Alfven waves via resonant interaction. We discuss effects of nonresonant Alfven waves on energy diffusion by using test particle simulations. When the Alfven waves are given at wavenumbers larger than the resonant wavenumber with small amplitude, simulated diffusion coefficient is similar to that by the quasi-linear theory. If the Alfven waves are added at wavenumbers smaller than the resonant wavenumber, it is found that the simulated diffusion coefficient exceeds the quasi-linear one and becomes larger with increasing the energy density of the nonresonant Alfven waves. (author)
The use of Alfven waves in NET
International Nuclear Information System (INIS)
A number of features of Alfven wave heating make it potentially attractive for use in large tokamac reactors. Among them are the availability and relatively low cost of the power supplies, the potential ability to act selectively on the current profile, and the probable absence of operational limits in size, fields or density. (author) 26 figs., 10 tabs., 54 refs
The nonlinear compressional Alfven wave equation
International Nuclear Information System (INIS)
The nonlinear wave equation of the compressional Alfven mode is derived in Lagrangian fluid coordinate. The nonlinearity attributes unequal weight to the terms of temporal and spatial derivatives. Two specific solutions relevant to transit-time magnetic pumping plasma heating and theta-pinch implosions are given. (Author)
Particle energization and current sheets in Alfvenic plasma turbulence
Makwana, Kirit; Li, Hui; Guo, Fan; Daughton, William; Cattaneo, Fausto
2015-11-01
Plasma turbulence is driven by injecting energy at large scales through stirring or instabilities. This energy cascades forward to smaller scales by nonlinear interactions, described by magnetohydrodynamics (MHD) at scales larger than the ion gyroradius. At smaller scales, the fluid description of MHD breaks down and kinetic mechanisms convert turbulent energy into particle energy. We investigate this entire process by simulating the cascade of strongly interacting Alfven waves using MHD and particle-in-cell (PIC) simulations. The plasma beta is varied and particle heating is analyzed. Anisotropic heating of particles is observed. We calculate the fraction of injected energy converted into non-thermal energy. At low beta we obtain a significant non-thermal component to the particle energy distribution function. We investigate the mechanisms behind this acceleration. The velocity distribution function is correlated with the sites of turbulent current sheets. The different dissipative terms due to curvature drift, gradB drift, polarization drifts, and parallel current density are also calculated. This has applications for understanding particle energization in turbulent space plasmas.
Alfven waves: a journey between space and fusion plasmas
International Nuclear Information System (INIS)
Alfven waves discovered by Hannes Alfven (1942 Nature 150 405) are fundamental electromagnetic oscillations in magnetized plasmas existing in the nature and laboratories. Alfven waves play important roles in the heating, stability and transport of plasmas. The anisotropic nearly incompressible shear Alfven wave is particularly interesting since, in realistic non-uniform plasmas, its wave spectra consist of both the regular discrete and the singular continuous components. In this Alfven lecture, I will discuss these spectral properties and examine their significant linear and nonlinear physics implications. These discussions will be based on perspectives from my own research in both space and laboratory fusion plasmas, and will demonstrate the positive feedback and cross-fertilization between these two important sub-disciplines of plasma physics research. Some open issues of nonlinear Alfven wave physics in burning fusion as well as magnetospheric space plasmas will also be explored.
Stationary nonlinear Alfven waves and solitons
Hada, T.; Kennel, C. F.; Buti, B.
1989-01-01
Stationary solutions of the derivative nonlinear Schroedinger equation are discussed and classified by using a pseudopotential formulation. The solutions consist of a rich family of nonlinear Alfven waves and solitons with parallel and oblique propagation directions. Expressions for the envelope and the phase of nonlinear waves with periodic envelope modulation, and 'hyperbolic' and 'algebraic' solitons are given. The propagation angle for the slightly modulated elliptic, periodic waves and for oblique solitons is evaluated.
Refined critical balance in strong Alfvenic turbulence
Mallet, A.; Schekochihin, A. A.; Chandran, B. D. G.
2014-01-01
We present numerical evidence that in strong Alfvenic turbulence, the critical balance principle---equality of the nonlinear decorrelation and linear propagation times---is scale invariant, in the sense that the probability distribution of the ratio of these times is independent of scale. This result only holds if the local alignment of the Elsasser fields is taken into account in calculating the nonlinear time. At any given scale, the degree of alignment is found to increase with fluctuation...
Alfven wave studies on a tokamak
International Nuclear Information System (INIS)
The continuum modes of the shear Alfven resonance are studied on the Tokapole II device, a small tokamak operated in a four node poloidal divertor configuration. A variety of antenna designs and the efficiency with which they deliver energy to the resonant layer are discussed. The spatial structure of the driven waves is studied by means of magnetic probes inserted into the current channel. In an attempt to optimize the coupling of energy in to the resonant layer, the angle of antenna currents with respect to the equilibrium field, antenna size, and plasma-to-antenna distance are varied. The usefulness of Faraday shields, particle shields, and local limiters are investigated. Antennas should be well shielded, either a dense Faraday shield or particle shield being satisfactory. The antenna should be large and very near to the plasma. The wave magnetic fields measured show a spatial resonance, the position of which varies with the value of the equilibrium field and mass density. They are polarized perpendicular to the equilibrium field. A wave propagates radially in to the resonant surface where it is converted to the shear Alfven wave. The signal has a short risetime and does not propagate far toroidally. These points are all consistent with a strongly damped shear Alfven wave. Comparisons of this work to theoretical predictions and results from other tokamaks are made
Saturation of Alfven modes in tokamaks
White, Roscoe; Gorelenkov, Nikolai; Gorelenkova, Marina; Podesta, Mario; Chen, Yang
2015-11-01
The effect of Alfven modes on high energetic particles in tokamaks is important in general, and could be of significance for ITER. This work is a combination of analytic models and numerical simulation to find the saturation levels of unstable Alfven modes and the resulting effect on beam and alpha particle distributions. Solving the drift kinetic equation with a guiding center code in the presence of Alfven modes driven unstable by a distribution of high energy particles requires the use of a δf formalism, wherby the initial distribution f0 is assumed to be a steady state high energy particle distribution in the absense of the modes, and f =f0 + δf describes the particle distribution in the presence of the modes. The Hamiltonian is written as H =H0 +H1 with H0 giving the unperturbed motion, conserving particle energy E, toroidal canonical momentum Pζ, and magnetic moment μ. By writing the initial particle distribution in terms of these variables, a simple means of calculating mode-particle energy and momentum transfer results, giving a very accurate δf formalism.
Excitation of Alfven Waves and Pulsar Radio Emission
Lyutikov, Maxim
1999-01-01
We analyze mechanisms of the excitation of Alfv\\'{e}n wave in pulsar magnetospheres as a possible source of pulsar radio emission generation. We find that Cherenkov excitation of obliquely propagating Alfv\\'{e}n waves is inefficient, while excitation at the anomalous cyclotron resonance by the particles from the primary beam and from the tail of the bulk distribution function may have a considerable growth rate. The cyclotron instability on Alfv\\'{e}n waves occurs in the kinetic regime still ...
Eigenmode Splitting in all Hydrogenated Amorphous Silicon Nitride Coupled Microcavity
Institute of Scientific and Technical Information of China (English)
ZHANG Xian-Gao; HUANG Xin-Fan; CHEN Kun-Ji; QIAN Bo; CHEN San; DING Hong-Lin; LIU Sui; WANG Xiang; XU Jun; LI Wei
2008-01-01
Hydrogenated amorphous silicon nitride based coupled optical microcavity is investigated theoretically and experimentally. The theoretical calculation of the transmittance spectra of optical microcavity with one cavity and coupled microcavity with two-cavity is performed.The optical eigenmode splitting for coupled microcavity is found due to the interaction between the neighbouring localized cavities.Experimentally,the coupled cavity samples are prepared by plasma enhanced chemical vapour deposition and characterized by photoluminescence measurements.It is found that the photoluminescence peak wavelength agrees well with the cavity mode in the calculated transmittance spectra.This eigenmode splitting is analogous to the electron state energy splitting in diatom molecules.
International Nuclear Information System (INIS)
With the first injection of neutral beams into the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40, 557 (2000)], a broad spectrum of fluctuations consisting of nearly equally spaced peaks in the frequency range from about 0.2 to 1.2 times the ion cyclotron frequency was observed. The frequencies scale with toroidal field and plasma density consistently with Alfven waves. From these and other observations, the modes have been identified as compressional Alfven eigenmodes (CAE). It has also recently been found that the ratio of the measured ion and electron temperatures in NSTX during neutral beam heating is anomalously high [Bell, Bull. Am. Phys. Soc. 46, 206 (2001)]. To explain the anomaly in the ratio of ion to electron temperature, it has been suggested that the CAE, driven by the beam ions, stochastically heat the thermal ions [Gates et al., Phys. Rev. Lett. 87, 205003 (2001)]. In this paper it is shown through studies of the power balance that stochastic heating of the thermal ions by the observed CAE alone is not solely responsible for the anomaly in the ion to electron temperature ratio
International Nuclear Information System (INIS)
The combined plasma non-uniformity effects on the energy deposition of Alfven waves launched by an external antenna in pre-heated spherical tokamaks are investigated. The following relevant physical processes are here possible: (a) the emergence of gaps in the shear Alfven continuum spectrum and the generation of discrete global Alfven eigenmodes with frequencies inside the gaps; (b) multi-wave interactions, interactions of gaps of the same kind (e.g., toroidicity induced) and of different kinds (toroidicity, ellipticity and triangularity induced) as well as of secondary order gaps arising when a pair of modes is coupled to one or more modes through other coupling parameters; (c) basic wave-plasma interactions as propagation, reflection, mode-conversion, tunneling and deposition. Thus, we solved numerically the full 2D wave equations for the vector and scalar potentials, using a quite general two-fluid resistive tensor-operator, without any geometrical limitations. The results obtained indicate the existence of antenna-launched wave characteristics for which the power is most efficiently coupled in outer regions of plasmas, which is of special interest for low aspect ratio tokamaks, e.g., for the generation of non-inductive current drive as well as for turbulence suppression and transport barriers formation
Fast-ion transport induced by Alfvén eigenmodes in the ASDEX Upgrade tokamak
DEFF Research Database (Denmark)
Garcia-Munoz, M.; Classen, I.G.J.; Geiger, B.;
2011-01-01
A comprehensive suite of diagnostics has allowed detailed measurements of the Alfvén eigenmode (AE) spatial structure and subsequent fast-ion transport in the ASDEX Upgrade (AUG) tokamak [1]. Reversed shear Alfvén eigenmodes (RSAEs) and toroidal induced Alfvén eigenmodes (TAEs) have been driven u...
Energy transfer between eigenmodes in multimodal atomic force microscopy
International Nuclear Information System (INIS)
We present experimental and computational investigations of tetramodal and pentamodal atomic force microscopy (AFM), respectively, whereby the first four or five flexural eigenmodes of the cantilever are simultaneously excited externally. This leads to six to eight additional observables in the form of amplitude and phase signals, with respect to the monomodal amplitude modulation method. We convert these additional observables into three or four dissipation and virial expressions, and show that these quantities can provide enhanced contrast that would otherwise remain hidden in the original observables. We also show that the complexity of the multimodal impact leads to significant energy transfer between the active eigenmodes, such that the dissipated power for individual eigenmodes may be positive or negative, while the total dissipated power remains positive. These results suggest that the contrast of individual eigenmodes in multifrequency AFM should be not be considered in isolation and that it may be possible to use different eigenfrequencies to probe sample properties that respond to different relaxation times. (paper)
Nonlinear propagation of short wavelength drift-Alfven waves
DEFF Research Database (Denmark)
Shukla, P. K.; Pecseli, H. L.; Juul Rasmussen, Jens
1986-01-01
Making use of a kinetic ion and a hydrodynamic electron description together with the Maxwell equation, the authors derive a set of nonlinear equations which governs the dynamics of short wavelength ion drift-Alfven waves. It is shown that the nonlinear drift-Alfven waves can propagate as two...
Effect of longitudinal modulation of Alfven wave filamentation
International Nuclear Information System (INIS)
The modulation of circularly polarized Alfven waves due to quasitransverse perturbations is addressed, and the nonlinear dynamics simulated numerically. In some instances, radial collapse (filamentation) of Alfven waves can be arrested by the magnetosonic waves stirred by the ponderomotive force. Such waves may, however, develop sharp fronts leading to strong hydrodynamic effects
A study of Alfven's ionizing critical velocity
International Nuclear Information System (INIS)
Alfven's hypothesis of the ionizing critical velocity is investigated on the basis of observations with rotating plasma devices. The experimental fact is that the relative velocity between a neutral gas and a plasma perpendicular to a magnetic field does not exceed a critical velocity vc = √2eVi/m (eVi and m, the ionization energy and the atomic or molecular mass of the gas, respectively). It is interpreted from the standpoint of a current which generates in a process of plasma polarization. A final interpretation on the hypothesis is not given, but the structure and elementary process of the ionizing interaction is clarified. (author)
Solitary kinetic Alfven waves in adiabatic process
International Nuclear Information System (INIS)
Solitary kinetic Alfven waves (SKAWs) have been an important subject in the field of space plasma physics because of their nonzero parallel electrical field and density fluctuations. Under different thermodynamic processes, SKAWs, within the limit of small amplitude, are studied analytically and numerically using the Sagdeev potential method. The results show that the width of the solitary structures is larger and the amplitude of the density humps is smaller under constant entropy than those under constant temperature with other relevant parameters being the same. The perturbed electromagnetic fields Ex, By, and Ez are also studied further.
HLL Riemann Solvers and Alfven Waves in Black Hole Magnetospheres
Punsly, Brian; Kim, Jinho; Garain, Sudip
2016-01-01
In the magnetosphere of a rotating black hole, an inner Alfven critical surface (IACS) must be crossed by inflowing plasma. Inside the IACS, Alfven waves are inward directed toward the black hole. The majority of the proper volume of the active region of spacetime (the ergosphere) is inside of the IACS. The charge and the totally transverse momentum flux (the momentum flux transverse to both the wave normal and the unperturbed magnetic field) are both determined exclusively by the Alfven polarization. However, numerical simulations of black hole magnetospheres are often based on 1-D HLL Riemann solvers that readily dissipate Alfven waves. Elements of the dissipated wave emerge in adjacent cells regardless of the IACS, there is no mechanism to prevent Alfvenic information from crossing outward. Thus, it is unclear how simulated magnetospheres attain the substantial Goldreich-Julian charge density associated with the rotating magnetic field. The HLL Riemann solver is also notorious for producing large recurring...
Nonlinear standing Alfven wave current system at Io: Theory
International Nuclear Information System (INIS)
We present a nonlinear analytical model of the Alfven current tubes continuing the currents through Io (or rather its ionosphere) generated by the unipolar inductor effect due to Io's motion relative to the magnetospheric plasma. We thereby extend the linear work by Drell et al. (1965) to the fully nonlinear, sub-Alfvenic situation also including flow which is not perpendicular to the background magnetic field. The following principal results have been obtained: (1) The portion of the currents feeding Io is aligned with the Alfven characteristics at an angle theta/sub A/ is the Alfven Mach number. (2) The Alfven tubes act like an external conductance Σ/sub A/=1/(μ0V/sub A/(1+M/sub A/2+2M/sub A/ sin theta)/sup 1/2/ where V/sub A/ is the Alfven wave propagation. Hence the Jovian ionospheric conductivity is not necessary for current closure. (3) In addition, the Alfven tubes may be reflected from either the torus boundary or the Jovian ionosphere. The efficiency of the resulting interaction with these boundaries varies with Io position. The interaction is particularly strong at extreme magnetic latitudes, thereby suggesting a mechanism for the Io control of decametric emissions. (4) The reflected Alfven waves may heat both the torus plasma and the Jovian ionosphere as well as produce increased diffusion of high-energy particles in the torus. (5) From the point of view of the electrodynamic interaction, Io is unique among the Jovian satellites for several reasons: these include its ionosphere arising from ionized volcanic gases, a high external Alfvenic conductance Σ/sub A/, and a high corotational voltage in addition to the interaction phenomenon with a boundary. (6) We find that Amalthea is probably strongly coupled to Jupiter's ionosphere while the outer Galilean satellites may occasionally experience super-Alfvenic conditions
Excitation of Alfven Cyclotron Instability by charged fusion products in tokamaks
International Nuclear Information System (INIS)
The spectrum of ion cyclotron emission (ICE) observed in tokamak experiments shows narrow peaks at multiples of the edge cyclotron frequency of background ions. A possible mechanism of ICE based on the fast Alfven Cyclotron Instability (ACI) resonantly excited by high energy charged products (α-particles or protons) is studied here. The two-dimensional ACI eigenmode structure and eigenfrequency are obtained in the large tokamak aspect ratio limit. The ACI is excited via wave-particle resonances in phase space by tapping the fast ion velocity space free energy. The instability growth rates are computed perturbatively from the perturbed fast particle distribution function, which is obtained by integrating the high frequency gyrokinetic equation along the particle orbit. Numerical examples of ACI growth rates are presented for TFTR plasmas. The fast ion distribution function is assumed to be singular in pitch angle near the plasma edge. The results are employed to understand the ICE in Deuterium-Deuterium (DD) and Deuterium-tritium (DT) tokamak experiments
Selecting method of the dominant eigenmodes of eddy currents for plasma control study
International Nuclear Information System (INIS)
A method for selecting the dominant eigenmodes of the eddy currents which affect plasma equilibria and its control is presented. The method is based on the blockline diagram analysis of a control model. The passive effects of conductors due to eddy currents are classified into 6 groups and each effect such as a shell effect and a shield effect is expressed in a simple summation of that of each eigenmode. This property is used to select the dominant eigenmodes for a plasma control study. The application of this method is made for JT-60 and 35 dominant eigenmodes are selected from among 464 eigenmodes obtained from the eddy current analysis. The effect due to these 35 dominant eigenmodes approximates well to that due to 464 eigenmodes and it is shown that the dimension of the control model is well reduced by using this method. (author)
Kinetic effects on Alfven wave nonlinearity. II. The modified nonlinear wave equation
International Nuclear Information System (INIS)
The study of kinetic effects on Alfven wave nonlinearity is continued. Previously obtained expressions for the perturbed (by an Alfven wave) ion and electron distribution functions are used to obtain a nonlinear wave equation for parallel-propagating, circularly polarized waves. The results are cast in the form of a modified version of the familiar derivative nonlinear Schroedinger equation. The approach in obtaining this equation is a hybrid one; fluid theory is used to the greatest extent possible, and kinetic theory is introduced where the correction is believed to be most important. Fluid theory at two levels of sophistication is employed. The first uses a simple scalar pressure term. This approach yields physical insight and illuminates the field-aligned fluid flow and the associated plasma density perturbation as a major contributor to Alfven wave nonlinearity. The second approach employs a tensor pressure term that in general will be necessary. The results indicate that kinetic effects in general produce a nonlinear wave equation that is of a different functional form than the derivative nonlinear Schroedinger equation, as previously reported by Mjolhus and Wyller [Phys. Scr. 33, 442 (1986); J. Plasma Phys. 40, 229 (1988)]. The coefficient of the derivative cubic term depends on the plasma beta in a way which, in general, is quite different from the fluid expression. In addition, a functionally novel term appears in the modified equation. The magnitude of this term, named the ''nonlocal term'' by Mjolhus and Wyller, can be large when the plasma beta is comparable to unity. The susceptibility of the modified equation to modulational instability is studied. Kinetic effects cause modulational instability of wave packets, even when fluid theory would predict modulational stability. This modulational instability occurs for both right- and left-hand polarized waves
Kinetic Alfv\\'{e}n solitary and rogue waves in superthermal plasmas
Bains, A; Xia, L -D
2014-01-01
We investigate the small but finite amplitude solitary Kinetic Alfv\\'{e}n waves (KAWs) in low $\\beta$ plasmas with superthermal electrons modeled by a kappa-type distribution. A nonlinear Korteweg-de Vries (KdV) equation describing the evolution of KAWs is derived by using the standard reductive perturbation method. Examining the dependence of the nonlinear and dispersion coefficients of the KdV equation on the superthermal parameter $\\kappa$, plasma $\\beta$ and obliqueness of propagation, we show that these parameters may change substantially the shape and size of solitary KAW pulses. Only sub-Alfv\\'enic, compressive solitons are supported. We then extend the study to examine kinetic Alfv\\'en rogue waves by deriving a nonlinear Schr\\"{o}dinger equation from {the KdV} equation. Rational solutions that form rogue wave envelopes are obtained. We examine how the behavior of rogue waves depends on the plasma parameters in question, finding that the rogue envelopes are lowered with increasing electron superthermal...
Embedded monopoles in quark eigenmodes in quenched SU(2) QCD
Chernodub, M N
2006-01-01
We study the embedded QCD monopoles (``quark monopoles'') using low-lying eigenmodes of the overlap Dirac operator in zero- and finite-temperature quenched SU(2) gauge theory on the lattice. These monopoles correspond to gauge-invariant hedgehogs in the quark-antiquark condensates. The monopoles were suggested to be agents of the chiral symmetry restoration since their cores should suppress the chiral condensate. We study numerically the scalar, axial and chirally invariant definitions of the embedded monopoles and show that the monopole densities are in fact globally anti-correlated with the density of the Dirac eigenmodes. We observe, that the embedded monopoles corresponding to low-lying Dirac eigenvalues are dense in the chirally invariant (high temperature) phase and dilute in the chirally broken (low temperature) phase. We find that the scaling of the scalar and axial monopole densities towards the continuum limit is similar to the scaling of the string-like objects while the chirally invariant monopole...
Cooperative eigenmodes and scattering in 1D atomic arrays
Bettles, R J; Adams, C S
2016-01-01
Using a classical coupled dipole model, we numerically investigate the cooperative behavior of a one dimensional array of atomic dipoles driven by a weak laser field. Changing the polarization and direction of the driving field allows us to separately address superradiant, subradiant, red shifted, and blue shifted eigenmodes, as well as observe strong Fano-like interferences between different modes. The cooperative eigenvectors can be characterized by the phase difference between nearest neighbor dipoles, ranging from all oscillating in phase to all oscillating out of phase with their nearest neighbors. Investigating the eigenvalue behavior as a function of atom number and lattice spacing, we find that certain eigenmodes of an infinite atomic chain have the same decay rate as a single atom between two mirrors.
Discrete space-time symmetry, polarization eigenmodes and their degeneracies
Potton, R J
2016-01-01
The irreducible representations of the group C4(direct product)V can be used to distinguish polarization eigenmodes, to account for their degeneracies and to associate them with particular magnetic crystal classes. The occurrence of this finite Abelian group points to a possible connection with topology but, irrespective of this, qualitative features of gyrotropy in condensed media can be approached in a way that does not depend on arbitrarily truncated tensor expansions.
Polyakov loop fluctuations in the Dirac eigenmode expansion
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-01-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal nontwisted periodic boundary condition for the link variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phases by numerical simulations in SU(3) quenched QCD. Thes...
Distortional eigenmodes and solutions for thin-walled beams
DEFF Research Database (Denmark)
Andreassen, Michael Joachim; Jönsson, Jeppe
2011-01-01
found for the homogeneous system the final uncoupled set of distortional differential equations including the load terms are presented and the full solution is given, including an illustrative example. This new approach is an alternative to the traditional first order GBT method....... differential equations for generalized beam theory (GBT), are determined via a semi-discretization procedure. The distortional displacement fields are found as solutions to a distortional homogeneous eigenvalue problem which produce distortional displacement eigenmodes. Using the distortional modal matrix...
Inertial Alfven waves in an inhomogeneous bi-Maxwellian plasma
International Nuclear Information System (INIS)
The Vlasov kinetic equation is solved using gyrokinetic theory and the dielectric tensor for non-relativistic, magnetized, bi-Maxwellian plasmas is calculated. A generalized dispersion relation for kinetic Alfven waves is derived taking into account the density inhomogeneity and temperature anisotropy. The modified dispersion relation thus obtained is then used to examine the propagation characteristics of the kinetic Alfven waves in the inertial regime. The importance of density inhomogeneity and temperature anisotropy for Solar corona is highlighted. The growth rate of the inertial Alfven wave proves that density inhomogeneity acts as a source of free energy.
Optical absorption and localization of eigenmodes in disordered clusters
International Nuclear Information System (INIS)
Results of a large-scale computational project for the calculation of the dispersion relations of eigenmodes (surface plasmons) and optical-absorption spectra of disordered clusters (fractal and uncorrelated) are reported. Fractals (cluster-cluster aggregates and the random-walk clusters, both original and diluted) and random-gas clusters consisting of 100--300 monomers are studied. High-accuracy results of Monte Carlo simulations are obtained. Transition of the eigenmodes from extremely localized to fully delocalized is found. Scaling of the dispersion relation of the eigenmodes, i.e., their localization radius or coherence length as a function of the spectral variable X, predicted earlier is quantitatively confirmed for diluted clusters. In contrast to the dispersion relations, the absorption spectra as functions of X do not show pronounced scaling in the intermediate region, but scale in the binary (spectral-wing) region. We suggest a new plot for the absorption profiles, namely absorption as a function of the coherence length of excitations. In such plots for most clusters, scaling is pronounced, but the indices differ dramatically from the predictions of the strong-localization theory. Possible reasons for the observed behavior are discussed
The Source of Alfven Waves That Heat the Solar Corona
Ruzmaikin, A.; Berger, M. A.
1998-01-01
We suggest a source for high-frequency Alfven waves invoked in coronal heating and acceleration of the solar wind. The source is associated with small-scale magnetic loops in the chromospheric network.
Multi-frequency tapping-mode atomic force microscopy beyond three eigenmodes in ambient air
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Santiago D. Solares
2014-09-01
Full Text Available We present an exploratory study of multimodal tapping-mode atomic force microscopy driving more than three cantilever eigenmodes. We present tetramodal (4-eigenmode imaging experiments conducted on a thin polytetrafluoroethylene (PTFE film and computational simulations of pentamodal (5-eigenmode cantilever dynamics and spectroscopy, focusing on the case of large amplitude ratios between the fundamental eigenmode and the higher eigenmodes. We discuss the dynamic complexities of the tip response in time and frequency space, as well as the average amplitude and phase response. We also illustrate typical images and spectroscopy curves and provide a very brief description of the observed contrast. Overall, our findings are promising in that they help to open the door to increasing sophistication and greater versatility in multi-frequency AFM through the incorporation of a larger number of driven eigenmodes, and in highlighting specific future research opportunities.
Confinement relevant Alfven instabilities in Wendelstein 7-AS
International Nuclear Information System (INIS)
Bursting Alfvenic activity accompanied by strong thermal crashes and frequency chirping in a W7-AS shot is studied. A theory explaining the experimental observations is developed. A novel mechanism of anomalous electron thermal conductivity is found. In addition, a general consideration of the influence of the gap crossing on the Alfven continuum in stellarators is carried out and a phenomenon of gap annihilation is predicted. (author)
Development of Alfven wave antenna system for TCABR Tokamak
International Nuclear Information System (INIS)
The advanced antenna system for Alfven wave plasma heating and current drive in TCABR tokamak is presented. The antenna system is capable of exciting the travelling waves M=- 1, N=-4, -6 with single helicity and provides the possibility to improve Alfven wave plasma heating efficiency and to increase RF power input up 1 MW, without an uncontrolled density rise. The basic features of the antenna design and the results of preliminary tests are analyzed. (author)
A laboratory search for plasma erosion by Alfven waves
Vincena, S.; Gekelman, W.; Pribyl, P.
2007-12-01
Obliquely propagating shear Alfven waves with transverse wavelengths on the order of the electron inertial length or even the ion gyro-radius are commonly observed in the earth's low-altitude auroral zones. These regions are also replete with observations of electron beams and transversely heated ions. A kinetic treatment of shear Alfven wave-particle interaction reveals how these waves can be responsible for some of the observed particle acceleration. The auroral plasma environment is further enriched by the presence of field-aligned depletions in plasma density, and it has been suggested* that the Alfven waves may, in fact, be the cause of the erosion of ionospheric density. In this laboratory experiment, shear waves will be launched using a variety of proven antennas, and also allowed to grow spontaneously as Drift-Alfven modes in seeded density depletions**. Detailed measurements of the wave magnetic fields in the perpendicular density gradient regions will be presented which demonstrate the generation of short perpendicular wave scales due to the perpendicular gradient in parallel wave phase speed. Miniature in-situ particle diagnostics will also be used to look for electron and ion acceleration. The waves will also be launched into an increasing region of background magnetic field in an attempt to model the ratios of Alfven speed to electron thermal speed, and density gradient scale length to electron inertial length appropriate to the earth's auroral zone. Preliminary results will be presented on the efficacy of shear Alfven waves to self-generate plasma density depletions, or deepen ambient density inhomogeneities. The experiments are conducted at UCLA's Basic Plasma Science Facility in the Large Plasma Device. *Chaston, et al., "Ionospheric erosion by Alfven Waves," JGR, V 111, A03206, 2006. **Penano, et al., "Drift-Alfven fluctuations associated with a narrow pressure striation," Phys. Plasmas, V 7, Issue 1, pp. 144-157 (2000).
Low-frequency waves in a high-beta collisionless plasma Polarization, compressibility and helicity
Gary, S. P.
1986-01-01
This paper considers the linear theory of waves near and below the ion cyclotron frequency in an isothermal electron-ion Vlasov plasma which is isotropic, homogeneous and magnetized. Numerical solutions of the full dispersion equation for the magnetosonic/whistler and Alfven/ion cyclotron modes at beta(i) = 1.0 are presented, and the polarizations, compressibilities, helicities, ion Alfven ratios and ion cross-helicities are exhibited and compared. At sufficiently large beta(i) and theta, the angle of propagation with respect to the magnetic field, the real part of the polarization of the Alfven/ion cyclotron wave changes sign, so that, for such parameters, this mode is no longer left-hand polarized. The Alfven/ion cyclotron mode becomes more compressive as the wavenumber increases, whereas the magnetosonic/whistler becomes more compressive with increasing theta.
Interplanetary Alfven waves and auroral (substorm) activity: IMP 8
International Nuclear Information System (INIS)
Almost year of IMP 8 interplanetary magnetic field and plasma data (Days 1-312, 1979) have been examined to determine the interplanetary causes of geomagnetic AE activity. The nature of the interplanetary medium (Alfvenic or non-Alfvenic) and the B2 correlation with AE were examined over 12-hour increments throughout the study. It is found that Alfvenic wave intervals (defined as Vx-Bx cross-correlation coefficients of >0.6) are present over 60% of the time and the southward component of the Alfven waves is well correlated with AE (average peak correlation coefficient 0.62), with a median lag of 43 min. The most probable delay of AE from Bs is considerably shorter, about 20-25 min. Southward magnetic fields during non-Alfvenic intervals (Vx-Bx cross-correlation coefficients of s were variable from event to event (and at different times within the Alfven wave train), ranging from 45 min to as little as 0 min. The cause of this variable delay is somewhat surprising and is not presently well understood
Localized eigenmodes of the overlap operator and their impact on the eigenvalue distribution
Energy Technology Data Exchange (ETDEWEB)
Hasenfratz, A.; Hoffmann, R. [Colorado Univ., Boulder, CO (United States). Department of Physics; Schaefer, S. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC
2007-09-15
In a system where chiral symmetry is spontaneously broken, the low energy eigenmodes of the continuum Dirac operator are extended. On the lattice, due to discretization effects, the Dirac operator can have localized eigenmodes that affect physical quantities sensitive to chiral symmetry. While the infrared eigenmodes of the Wilson Dirac operator are usually extended even on coarse lattices, the chiral overlap operator has many localized eigenmodes in the physical region, especially in mixed action simulations. Depending on their density, these modes can introduce strong lattice artifacts. The effect can be controlled by changing the parameters of the overlap operator, in particular the clover improvement term and the center of the overlap projection. (orig.)
International Nuclear Information System (INIS)
Stationary transonic super-Alfven, subsonic super-Alfven, supersonic sub-Alfven, and Alfven magnetohydrodynamic flows, obtained by numerical modeling of their build-up processes, in coaxial canals in the presence of longitudinal magnetic field have been considered
Inductive Eigenmodes of a resistive toroidal surface in vacuum
International Nuclear Information System (INIS)
In this paper it has been studied the Electro-Magnetic (EM) Eigenmodes, sufficiently slow as to legitimate the pre-Maxwell approximation of Maxwell's system (or inductive Eigenmodes), of a given smooth, toroidal-unknotted, electrically resistive surface Τ with given smooth (surface) resistivity 0 degree 3. Within the above limitations (to be made more precise), the geometry of Τ is arbitrary. With the eigenvalue associated with the generic Eigenmode being defined as the opposite of its logarithmic time-derivative, one expects that the resulting spectrum be discrete and strictly positive. It shall be interested into the degenerate case where Τ be cut (i.e. electrically broken) along one or more of its irreducible cycles. This case will be analyzed autonomously, rather than as a limit (for ρdegree → ∞ along the cuts) of the regular case. Without cuts, the Eigenproblem under consideration is nothing but the two-dimensional (2-dim) generalization of the classical case of a smooth, unknotted, electrically conductive, simple coil in infinite vacuum. Its analysis hinges on the classical potential theory, and turns out to be a special application of the linear, integrodifferential (elliptic) equation theory on a compact, multiply connected, 2-dim manifold. The attention and approach will be confined to strong (or classical) solutions, both in Τ and C Τ = R3 / Τ. This study is divided in two parts: a General Part (Sects 1 divided 4) is devoted to the case of generic Τ and ρdegree (within the convenient smoothness requirements), whereas a Special Part (Sects 5 divided 7) deals with the (more or less formal) discussion of a couple of particular cases (Τ ≡ a canonical torus), both of which with uniform ρdegree. Some propaedeutical/supplementary information is provided in a number of Appendices
Polyakov loop fluctuations in the Dirac eigenmode expansion
Doi, Takahiro M.; Redlich, Krzysztof; Sasaki, Chihiro; Suganuma, Hideo
2015-11-01
We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal nontwisted periodic boundary condition for the link variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phases by numerical simulations in SU(3) quenched QCD. These results indicate that there is no direct, one-to-one correspondence between confinement and chiral symmetry breaking in QCD in the context of different properties of the Polyakov loop fluctuation ratios.
Free-boundary toroidal Alfvén eigenmodes
Chen, Eugene Y.; Berk, H. L.; Breizman, B.; Zheng, L. J.
2011-05-01
A numerical study is presented for the n = 1 free-boundary toroidal Alfvén eigenmodes (TAE) in tokamaks, which shows that there is considerable sensitivity of n = 1 modes to the position of the conducting wall. An additional branch of the TAE is shown to emerge from the upper continuum as the ratio of conducting wall radius to plasma radius increases. Such phenomena arise in plasma equilibria with both circular and shaped cross sections, where the shaped profile studied here is similar to that found in Alcator C-Mod.
Optical Control of Fluorescence through Plasmonic Eigenmode Extinction
Xu, Xiaoying; Lin, Shih-Che; Li, Quanshui; Zhang, Zhili; Ivanov, Ilia N.; Li, Yuan; Wang, Wenbin; Gu, Baohua; Zhang, Zhenyu; Hsueh, Chun-Hway; Snijders, Paul C.; Seal, Katyayani
2015-04-01
We introduce the concept of optical control of the fluorescence yield of CdSe quantum dots through plasmon-induced structural changes in random semicontinuous nanostructured gold films. We demonstrate that the wavelength- and polarization dependent coupling between quantum dots and the semicontinuous films, and thus the fluorescent emission spectrum, can be controlled and significantly increased through the optical extinction of a selective band of eigenmodes in the films. This optical method of effecting controlled changes in the metal nanostructure allows for versatile functionality in a single sample and opens a pathway to in situ control over the fluorescence spectrum.
Optical Control of Fluorescence through Plasmonic Eigenmode Extinction
Xu, Xiaoying; Li, Quanshui; Zhang, Zhili; Ivanov, Ilia N; Li, Yuan; Wang, Wenbin; Gu, Baohua; Zhang, Zhenyu; Hsueh, Chun-Hway; Snijders, Paul C; Seal, Katyayani
2015-01-01
We introduce the concept of optical control of the fluorescence yield of CdSe quantum dots through plasmon-induced structural changes in random semicontinuous nanostructured gold films. We demonstrate that the wavelength- and polarization dependent coupling between quantum dots and the semicontinuous films, and thus the fluorescent emission spectrum, can be controlled and significantly increased through the optical extinction of a selective band of eigenmodes in the films. This optical method of effecting controlled changes in the metal nanostructure allows for versatile functionality in a single sample and opens a pathway to in situ control over the fluorescence spectrum.
Filamentation of dispersive Alfven waves in density channels: Hall magnetohydrodynamics description
International Nuclear Information System (INIS)
Filamentation of dispersive Alfven waves initiated by low or high density channels (depending on the plasma beta) is simulated numerically in the framework of ideal Hall magnetohydrodynamics, and asymptotically modeled with a two-dimensional nonlinear Schroedinger equation including a linear attracting potential. Compared with the dynamics in a homogeneous plasma, the phenomenon is accelerated and occurs for a broader range of parameters. In the case of an isolated channel with a width comparable to the pump wavelength, the transverse wave collapse can be replaced by a moderate amplification. In many cases, a relatively complex dynamics takes place, characterized by an oscillation between magnetic filaments and magnetic ribbons, leading to the formation of small scales at which dissipative effects could become relevant. Alfven vortices, governed by the equations of the reduced magnetohydrodynamics, are also identified in the simulations, in spite of their small amplitude relative to the wave. The formation of structures under the effect of periodic or random distributions of low and high density channels is also discussed
ARQ strategies for MIMO eigenmode transmission with adaptive modulation and coding
DEFF Research Database (Denmark)
De Carvalho, Elisabeth; Popovski, Petar
Packet retransmission strategies are presented for MIMO eigenmode transmission where adaptive modulation and coding (AMC) is implemented. The retransmission design is based on weighted linear MMSE. It includes the transmit and receiver filter, the power and eigenmode allocation and AMC level when...
Interacting Eigenmodes of a plasma diode with a density gradient
International Nuclear Information System (INIS)
The formation of narrow high frequency electric field spikes in plasma density gradients is investigated using one-dimensional particle in cell simulations. It is found that the shape of the plasma density gradient is very important for the spike formation. The spike appears also in simulations with immobile ions showing that a coupling to the ion motion, as for example in wave interactions, is not necessary for the formation of HF spikes. However, the HF spike influences the ion motion, and ion waves are seen in the simulations. It has been found, in experiments and simulations, that the electron velocity distribution function deviates from the Maxwellian distribution. Dispersion relations are calculated using realistic distribution functions. The spike can be seen as a coupled system of two Eigenmodes of a plasma diode fed by the beam-plasma interaction. Based on a simplified fluid description of such Eigenmodes, explanations for the localization of the spike, spatially and in frequency, are given. The density amplitude is comparable with the DC density level close to the cathode. Space charge limits of waves in this region seem to determine the amplitude of the spike through the Poisson's equation
Interacting Eigenmodes of a plasma diode with a density gradient
Energy Technology Data Exchange (ETDEWEB)
Loefgren, T.; Gunell, H.
1997-08-01
The formation of narrow high frequency electric field spikes in plasma density gradients is investigated using one-dimensional particle in cell simulations. It is found that the shape of the plasma density gradient is very important for the spike formation. The spike appears also in simulations with immobile ions showing that a coupling to the ion motion, as for example in wave interactions, is not necessary for the formation of HF spikes. However, the HF spike influences the ion motion, and ion waves are seen in the simulations. It has been found, in experiments and simulations, that the electron velocity distribution function deviates from the Maxwellian distribution. Dispersion relations are calculated using realistic distribution functions. The spike can be seen as a coupled system of two Eigenmodes of a plasma diode fed by the beam-plasma interaction. Based on a simplified fluid description of such Eigenmodes, explanations for the localization of the spike, spatially and in frequency, are given. The density amplitude is comparable with the DC density level close to the cathode. Space charge limits of waves in this region seem to determine the amplitude of the spike through the Poisson`s equation. 12 refs, 19 figs.
Stability criteria for current-driven drift wave eigenmodes
International Nuclear Information System (INIS)
Eigenmodes of current-driven collisionless electrostatic drift waves in a sheared magnetic field are re-examined in the light of the recent discovery that their non-current-driven counterparts are stable. Conditions for instability are determined from numerical finite difference and variational solutions of the slab model differential equation. It is found that three stringent conditions are required for instability: (1) very weak shear, (2) low ion temperature, and (3) very large parallel drift velocity. For L/sub n//L/sub s/=0.02 and T/sub i//T/sub e/=0, the instability threshold is u/sub d//c/sub s/=0.85, where L/sub n/ and L/sub s/ are the density and shear scale lengths, respectively, u/sub d/ is the drift velocity, and c/sub s/ is the sound speed. For larger shear and finite ion temperature the critical drift velocity is even larger. It is concluded that drift wave fluctuations in tokamaks cannot be described in terms of these eigenmodes
Tuan, P H; Wen, C P; Yu, Y T; Liang, H C; Huang, K F; Chen, Y F
2014-02-01
Experimentally resonant modes are commonly presumed to correspond to eigenmodes in the same bounded domain. However, the one-to-one correspondence between theoretical eigenmodes and experimental observations is never reached. Theoretically, eigenmodes in numerous classical and quantum systems are the solutions of the homogeneous Helmholtz equation, whereas resonant modes should be solved from the inhomogeneous Helmholtz equation. In the present paper we employ the eigenmode expansion method to derive the wave functions for manifesting the distinction between eigenmodes and resonant modes. The derived wave functions are successfully used to reconstruct a variety of experimental results including Chladni figures generated from the vibrating plate, resonant patterns excited from microwave cavities, and lasing modes emitted from the vertical cavity. PMID:25353549
Electromagnetic transport components and sheared flows in drift-Alfven turbulence
DEFF Research Database (Denmark)
Naulin, V.
2003-01-01
Results from three-dimensional numerical simulations of drift-Alfven turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma beta we ob...... folded Gaussian, while the PDFs of the spatially averaged transport are in good agreement with an extreme value distribution. (C) 2003 American Institute of Physics....... related to magnetic flutter is proposed. The characteristics of the ExB flux are investigated using probability density distribution functions (PDFs). Although they are not Gaussian, no signs of algebraic tails in the PDFs are observed. The PDFs of the pointwise transport are found to agree well with a...
Prokopenko, Yu. V.; Filippov, Yu. F.; Shipilova, I. A.
2007-09-01
A semicylindrical dielectric resonator with a thin cylindrical inhomogeneity in the region of the field antinode of a whispering gallery eigenmode has been studied. Characteristic equations determining the complex eigenfrequencies of such resonators with axially homogeneous eigenmodes are obtained. It is shown that the presence of a dielectric or conducting inhomogeneity leads to a frequency shift and causes additional energy losses of the eigenmode.
Stable Alfven wave dynamo action in the reversed field pinch
International Nuclear Information System (INIS)
Recent advances in linear resistive MHD stability analysis are used to calculate the quasi-linear dynamo mean electromotive force of Alfven waves. This emf is incorporated into a one-dimensional transport and mean-field evolution code. The changing equilibrium is then fed back to the stability code to complete a computational framework that self-consistently evaluates a dynamic plasma dynamo. Static quasi-linear Alfven wave calculations have shown that dynamo emfs on the order of eta vector J are possible. This suggested a possible explanation of RFP behavior and a new (externally driven) mechanism for extending operation and controlling field profiles (possibly reducing plasma transport). This thesis demonstrates that the dynamo emf can quickly induce plasma currents whose emf cancels the dynamo effect. This thesis also contains extensive studies of resistive Alfven wave properties. This includes behavior versus spectral location, magnetic Reynolds number and wave number
Alfven QPOs in magnetars in the anelastic approximation
Cerdá-Durán, Pablo; Font, José A
2009-01-01
We perform two-dimensional simulations of Alfven oscillations in magnetars, modeled as relativistic stars with a dipolar magnetic field. We use the anelastic approximation to general relativistic magnetohydrodynamics, which allows for an effective suppression of fluid modes and an accurate description of Alfven waves. In addition, we compute Alfven oscillation frequencies along individual magnetic field lines with a semi-analytic approach, employing a short-wavelength approximation. Our main findings are as follows: a) we confirm the existence of two families of quasi-periodic oscillations (QPOs), with harmonics at integer multiples of the fundamental frequency, as was found in the linear study of Sotani, Kokkotas & Stergioulas (2008); b) the QPOs appearing near the magnetic axis are split into two groups, depending on their symmetry across the equatorial plane. The antisymmetric QPOs have only odd integer-multiple harmonics; c) the continuum obtained with our semi-analytic approach agrees remarkably well...
Diffusive shock acceleration with magnetic field amplification and Alfvenic drift
Kang, Hyesung
2012-01-01
We explore how wave-particle interactions affect diffusive shock acceleration (DSA) at astrophysical shocks by performing time-dependent kinetic simulations, in which phenomenological models for magnetic field amplification (MFA), Alfvenic drift, thermal leakage injection, Bohm-like diffusion, and a free escape boundary are implemented. If the injection fraction of cosmic-ray (CR) particles is greater than 2x10^{-4}, for the shock parameters relevant for young supernova remnants, DSA is efficient enough to develop a significant shock precursor due to CR feedback, and magnetic field can be amplified up to a factor of 20 via CR streaming instability in the upstream region. If scattering centers drift with Alfven speed in the amplified magnetic field, the CR energy spectrum can be steepened significantly and the acceleration efficiency is reduced. Nonlinear DSA with self-consistent MFA and Alfvenic drift predicts that the postshock CR pressure saturates roughly at 10 % of the shock ram pressure for strong shocks...
Moore, R. L.; Hammer, R.; Musielak, Z. E.; Suess, S. T.; An, C.-H.
1992-01-01
In our recent analysis of Alfven wave reflection in solar coronal holes, we found evidence that coronal holes are heated by reflected Alfven waves. This result suggests that the reflection is inherent to the process that dissipates these Alfven waves into heat. We propose a novel dissipation process that is driven by the reflection, and that plausibly dominates the heating in coronal holes.
Alfven wave heating of current-carrying plasmas
International Nuclear Information System (INIS)
Alfven wave heating involves the excitation, by antenna currents, of MHD waves which mode convert to short wavelength quasi-electrostatic waves (QEW) at the Alfven resonance position. Over the past few years the authors developed the computer code ANTENNA which solves the kinetic theory equations that describe this process for a cylindrical model of a tokamak. Recently, the following improvements have been made to the code: Antennas with radial current elements can now be treated; arbitrary density and temperature profiles can be analysed; the kinetic theory wave equations have been formulated for arbitrary force-free plasma-current distributions
Ion temperature in plasmas with intrinsic Alfven waves
Wu, C. S.; Yoon, P. H.; Wang, C. B.
2014-10-01
This Brief Communication clarifies the physics of non-resonant heating of protons by low-frequency Alfvenic turbulence. On the basis of general definition for wave energy density in plasmas, it is shown that the wave magnetic field energy is equivalent to the kinetic energy density of the ions, whose motion is induced by the wave magnetic field, thus providing a self-consistent description of the non-resonant heating by Alfvenic turbulence. Although the study is motivated by the research on the solar corona, the present discussion is only concerned with the plasma physics of the heating process.
Global structures of Alfven-ballooning modes in magnetospheric plasmas
International Nuclear Information System (INIS)
The authors show that a steep plasma pressure gradient can lead to radially localized Alfven modes, which are damped through coupling to filed line resonances. These have been called drift Alfven balloning modes (DABM) and are the prime candidates to explain Pc4-Pc5 geomagnetic pulsations observed during storms. A strong dependence of the damping rate on the azimuthal wave number m is established, as well as on the equilibrium profile. A minimum azimuthal mode number can be found for the DABM to be radially trapped. The authors find that higher m DABMs are better localized, which is consistent with high-m observations
First Results of PIC Modeling of Kinetic Alfven Wave Dissipation
Chulaki, Anna; Hesse, Michael; Zenitani, Seiji
2007-01-01
We present first results of an investigation of the kinetic damping of Alfven wave turbulence. The methodology is based on a fully electromagnetic, three-dimensional, particle in cell code. The calculation is initialized by an Alfven wave spectrum. Subsequently, a cascade develops, and damping by coupling to both ions and electrons is observed. We discuss results of these calculations, and present first estimates of damping rates and of the effects of energy transfer on ion and electron distributions. The results pertain to solar wind heating and acceleration.
Resonant Alfven wave instabilities driven by streaming fast particles
International Nuclear Information System (INIS)
A plasma simulation code is used to study the resonant interactions between streaming ions and Alfven waves. The medium which supports the Alfven waves is treated as a single, one-dimensional, ideal MHD fluid, while the ions are treated as kinetic particles. The code is used to study three ion distributions: a cold beam; a monoenergetic shell; and a drifting distribution with a power-law dependence on momentum. These distributions represent: the field-aligned beams upstream of the earth's bow shock; the diffuse ions upstream of the bow shock; and the cosmic ray distribution function near a supernova remnant shock. 92 refs., 31 figs., 12 tabs
High and low frequency Alfven modes in tokamaks
International Nuclear Information System (INIS)
We present an analysis of the typical features of shear Alfven waves in tokamak plasmas in a frequency domain ranging from the ''high'' frequencies (ω ≅ νA/2qR0; νA being the Alfven speed and qR0 the tokamak connection length) of the toroidal gap to the ''low'' frequencies, comparable with the thermal ion diamagnetic frequency, ω*pi and/or the thermal ion transit frequency ωti = νti/qR0 (νti being the ion thermal speed). (author)
KINETIC ALFVEN WAVES EXCITED BY OBLIQUE MAGNETOHYDRODYNAMIC ALFVEN WAVES IN CORONAL HOLES
International Nuclear Information System (INIS)
Kinetic Alfven waves (KAWs) are small-scale dispersive AWs that can play an important role in particle heating and acceleration of space and solar plasmas. An excitation mechanism for KAWs created by the coupling between large-scale oblique AWs and small-scale KAWs is presented in this paper. Taking into account both the collisional and Landau damping dissipations, the results show that the net growth rate of the excited KAWs increases with their perpendicular wavenumber kperpendicular and reaches maximum at λe kperpendicular ∼ 0.3, where λe is the electron inertial length. However, for KAWs with shorter perpendicular wavelengths, the net growth rate decreases rapidly due to dissipative effects. The evaluation of the threshold amplitude of the AW implies that for KAWs with λe kperpendicular e kperpendicular < 0.3 can be not only efficiently excited in the interplume region but also strongly dissipated in the dense plume due to the Landau damping.
Studies of the Jet in BL Lacertae. II. Superluminal Alfv\\'en Waves
Cohen, M H; Arshakian, T G; Clausen-Brown, E; Homan, D C; Hovatta, T; Kovalev, Y Y; Lister, M L; Pushkarev, A B; Richards, J L; Savolainen, T
2014-01-01
Ridge lines on the pc-scale jet of the active galactic nucleus BL Lac display transverse patterns that move superluminally downstream. The patterns are not ballistic, but are analogous to waves on a whip. Their apparent speeds $\\beta_\\mathrm{app}$ (units of $c$) range from 4.2 to 13.5, corresponding to $\\beta_\\mathrm{wave}^\\mathrm{gal}= 0.981 - 0.998$ in the galaxy frame. We show that the magnetic field in the jet is well-ordered with a strong transverse component, and assume that it is helical and that the transverse patterns are longitudinal Alfv\\'en waves. The wave-induced transverse speed of the jet is non-relativistic ($\\beta_\\mathrm{tr}^\\mathrm{gal}\\sim 0.09$) and in agreement with our assumption of low-amplitude waves. In 2010 the wave activity subsided and the jet displayed a mild wiggle that had a complex oscillatory behavior. The waves are excited by changes in the position angle of the recollimation shock, in analogy to exciting a wave on a whip by shaking it. Simple models of the system are presen...
Eigenmodes of quasi-static magnetic islands in current sheet
International Nuclear Information System (INIS)
As observation have shown, magnetic islands often appear before and/or after the onset of magnetic reconnections in the current sheets, and they also appear in the current sheets in the solar corona, Earth's magnetotail, and Earth's magnetopause. Thus, the existence of magnetic islands can affect the initial conditions in magnetic reconnection. In this paper, we propose a model of quasi-static magnetic island eigenmodes in the current sheet. This model analytically describes the magnetic field structures in the quasi-static case, which will provide a possible approach to reconstructing the magnetic structures in the current sheet via observation data. This model is self-consistent in the kinetic theory. Also, the distribution function of charged particles in the magnetic island can be calculated.
An improved perfectly matched layer for the eigenmode expansion technique
DEFF Research Database (Denmark)
Gregersen, Niels; Mørk, Jesper
2008-01-01
When performing optical simulations for rotationally symmetric geometries using the eigenmode expansion technique, it is necessary to place the geometry under investigation inside a cylinder with perfectly conducting walls. The parasitic reflections at the boundary of the computational domain can...... be suppressed by introducing a perfectly matched layer (PML) using e.g. complex coordinate stretching of the cylinder radius. However, the traditional PML suffers from an artificial field divergence limiting its usefulness. We show that the choice of a constant cylinder radius leads to mode profiles...... with exponentially increasing field amplitudes resulting in numerical instability. As a remedy we propose an improved PML based on a mode-dependent cylinder radius and mode profiles with stable field amplitudes. The new PML formulation eliminates the artificial field divergence and ensures numerical...
Numerical study of Alfvén eigenmodes in the Experimental Advanced Superconducting Tokamak
International Nuclear Information System (INIS)
Alfvén eigenmodes in up-down asymmetric tokamak equilibria are studied by a new magnetohydrodynamic eigenvalue code. The code is verified with the NOVA code for the Solovév equilibrium and then is used to study Alfvén eigenmodes in a up-down asymmetric equilibrium of the Experimental Advanced Superconducting Tokamak. The frequency and mode structure of toroidicity-induced Alfvén eigenmodes are calculated. It is demonstrated numerically that up-down asymmetry induces phase variation in the eigenfunction across the major radius on the midplane
Alfv\\'enic instabilities driven by runaways in fusion plasmas
Fülöp, T
2014-01-01
Runaway particles can be produced in plasmas with large electric fields. Here we address the possibility that such runaway ions and electrons excite Alfv\\'enic instabilities. The magnetic perturbation induced by these modes can enhance the loss of runaways. This may have important implications for the runaway electron beam formation in tokamak disruptions.
Nonlinear Alfven waves and solitons in cold plasma
International Nuclear Information System (INIS)
A finite-zone sector for the derivative nonlinear Schroedinger equation, which describes nonlinear small-amplitude. Alfven waves in the long-wave approximation, is investigated. The formulas for periodic one-phase and one-soliton solutions and the general formula for an n-soliton solution envelope are obtained
Quantum effects on compressional Alfven waves in compensated semiconductors
Energy Technology Data Exchange (ETDEWEB)
Amin, M. R. [Department of Electronics and Communications Engineering, East West University, Aftabnagar, Dhaka 1212 (Bangladesh)
2015-03-15
Amplitude modulation of a compressional Alfven wave in compensated electron-hole semiconductor plasmas is considered in the quantum magnetohydrodynamic regime in this paper. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential in the momentum balance equations of the charge carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the compressional Alfven wave by employing the standard reductive perturbation technique. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the linear and nonlinear dispersions of the compressional Alfven wave. Detailed analysis of the modulation instability in the long-wavelength regime is presented. For typical parameter ranges of the semiconductor plasmas and at the long-wavelength regime, it is found that the wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the effect of the Bohm potential may be neglected in comparison with the effect of the exchange-correlation potential in the linear and nonlinear dispersions of the compressional Alfven wave.
Drift-Alfven vortices in Hamiltonian plasma fluids
International Nuclear Information System (INIS)
Plasma phenomena with frequencies below the ion cyclotron and the magnetosonic and above the ion-acoustic frequency are discussed. Finite electron mass and ion gyro-radius effects are taken into account. Equilibrium and stability are investigated from a noncanonical Hamiltonian point of view. Explicit solutions are given for dipole drift-Alfven vortices that propagate across a uniform magnetic field
ALFVEN WAVES IN A PARTIALLY IONIZED TWO-FLUID PLASMA
Energy Technology Data Exchange (ETDEWEB)
Soler, R.; Ballester, J. L.; Terradas, J. [Departament de Fisica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain); Carbonell, M., E-mail: roberto.soler@uib.es, E-mail: joseluis.ballester@uib.es, E-mail: jaume.terradas@uib.es, E-mail: marc.carbonell@uib.es [Departament de Matematiques i Informatica, Universitat de les Illes Balears, E-07122 Palma de Mallorca (Spain)
2013-04-20
Alfven waves are a particular class of magnetohydrodynamic waves relevant in many astrophysical and laboratory plasmas. In partially ionized plasmas the dynamics of Alfven waves is affected by the interaction between ionized and neutral species. Here we study Alfven waves in a partially ionized plasma from the theoretical point of view using the two-fluid description. We consider that the plasma is composed of an ion-electron fluid and a neutral fluid, which interact by means of particle collisions. To keep our investigation as general as possible, we take the neutral-ion collision frequency and the ionization degree as free parameters. First, we perform a normal mode analysis. We find the modification due to neutral-ion collisions of the wave frequencies and study the temporal and spatial attenuation of the waves. In addition, we discuss the presence of cutoff values of the wavelength that constrain the existence of oscillatory standing waves in weakly ionized plasmas. Later, we go beyond the normal mode approach and solve the initial-value problem in order to study the time-dependent evolution of the wave perturbations in the two fluids. An application to Alfven waves in the low solar atmospheric plasma is performed and the implication of partial ionization for the energy flux is discussed.
1.5D quasilinear model and its application on beams interacting with Alfvén eigenmodes in DIII-D
Ghantous, K.; Gorelenkov, N. N.; Berk, H. L.; Heidbrink, W. W.; Van Zeeland, M. A.
2012-09-01
We propose a model, denoted here by 1.5D, to study energetic particle (EP) interaction with toroidal Alfvenic eigenmodes (TAE) in the case where the local EP drive for TAE exceeds the stability limit. Based on quasilinear theory, the proposed 1.5D model assumes that the particles diffuse in phase space, flattening the pressure profile until its gradient reaches a critical value where the modes stabilize. Using local theories and NOVA-K simulations of TAE damping and growth rates, the 1.5D model calculates the critical gradient and reconstructs the relaxed EP pressure profile. Local theory is improved from previous study by including more sophisticated damping and drive mechanisms such as the numerical computation of the effect of the EP finite orbit width on the growth rate. The 1.5D model is applied on the well-diagnosed DIII-D discharges #142111 [M. A. Van Zeeland et al., Phys. Plasmas 18, 135001 (2011)] and #127112 [W. W. Heidbrink et al., Nucl. Fusion. 48, 084001 (2008)]. We achieved a very satisfactory agreement with the experimental results on the EP pressure profiles redistribution and measured losses. This agreement of the 1.5D model with experimental results allows the use of this code as a guide for ITER plasma operation where it is desired to have no more than 5% loss of fusion alpha particles as limited by the design.
Fligsen, T; Van Rienen, U
2014-01-01
The computation of eigenmodes for complex accelerating structures is a challenging and important task for the design and operation of particle accelerators. Discretizing long and complex structures to determine its eigenmodes leads to demanding computations typically performed on super computers. This contribution presents an application example of a method to compute eigenmodes and other parameters derived from these eigenmodes for long and complex structures using standard workstation computers. This is accomplished by the decomposition of the complex structure into several single segments. In a next step, the electromagnetic properties of the segments are described in terms of a compact state-space model. Subsequently, the state-space models of the single structures are concatenated to the full structure. The results of direct calculations are compared with results obtained by the concatenation scheme in terms of computational time and accuracy.
Hammer, Manfred
2004-01-01
The propagation of guided and nonconfined optical waves at fixed frequency through dielectric structures with piecewise constant, rectangular permittivity is considered in two spatial dimensions. Bidirectional versions of eigenmodes, computed for sequences of multilayer slab waveguides, constitute t
Hammer, Manfred; Honsa, R.; Richter, L.
2003-01-01
Superpositions of two perpendicularly oriented bidirectional eigenmode propagation (BEP) fields, composed of basis modes that satisfy Dirichlet boundary conditions, can establish rigorous semianalytical solutions for problems of 2-D fixed-frequency wave propagation on unbounded, cross-shaped domains
Inductive Eigenmodes of a resistive toroidal surface in vacuum
Energy Technology Data Exchange (ETDEWEB)
Lo Surdo, C. [ENEA, Centro Ricerche Frascati, Rome (Italy). Dipt. Innovazione
1999-07-01
In this paper it has been studied the Electro-Magnetic (EM) Eigenmodes, sufficiently slow as to legitimate the pre-Maxwell approximation of Maxwell's system (or inductive Eigenmodes), of a given smooth, toroidal-un knotted, electrically resistive surface {tau} with given smooth (surface) resistivity 0 < {rho}{sub d}egree < {infinity}, and lying in the (empty) R{sup 3}. Within the above limitations (to be made more precise), the geometry of {tau} is arbitrary. With the eigenvalue associated with the generic Eigenmode being defined as the opposite of its logarithmic time-derivative, one expects that the resulting spectrum be discrete and strictly positive. It shall be interested into the degenerate case where {tau} be cut (i.e. electrically broken) along one or more of its irreducible cycles. This case will be analyzed autonomously, rather than as a limit (for {rho}{sub d}egree {yields} {infinity} along the cuts) of the regular case. Without cuts, the Eigenproblem under consideration is nothing but the two-dimensional (2-dim) generalization of the classical case of a smooth, unknotted, electrically conductive, simple coil in infinite vacuum. Its analysis hinges on the classical potential theory, and turns out to be a special application of the linear, integrodifferential (elliptic) equation theory on a compact, multiply connected, 2-dim manifold. The attention and approach will be confined to strong (or classical) solutions, both in {tau} and C {tau} = R{sup 3} / {tau}. This study is divided in two parts: a General Part (Sects 1 divided 4) is devoted to the case of generic {tau} and {rho}{sub d}egree (within the convenient smoothness requirements), whereas a Special Part (Sects 5 divided 7) deals with the (more or less formal) discussion of a couple of particular cases ({tau} {identical_to} a canonical torus), both of which with uniform {rho}{sub d}egree. Some propaedeutical/supplementary information is provided in a number of Appendices. [Italian] Il presente
Multiple regimes of operation in bimodal AFM: understanding the energy of cantilever eigenmodes
Daniel Kiracofe; Arvind Raman; Dalia Yablon
2013-01-01
One of the key goals in atomic force microscopy (AFM) imaging is to enhance material property contrast with high resolution. Bimodal AFM, where two eigenmodes are simultaneously excited, confers significant advantages over conventional single-frequency tapping mode AFM due to its ability to provide contrast between regions with different material properties under gentle imaging conditions. Bimodal AFM traditionally uses the first two eigenmodes of the AFM cantilever. In this work, the authors...
Theory and calculation of finite beta drift wave turbulence
International Nuclear Information System (INIS)
Using numerical techniques, we calculate eigenmodes of the nonlinear universal mode with finite beta in order to determine the scaling of the saturation level of the instability with beta. We use two different renormalizations in the calculations and find that using the appropriate renormalization, we are able to recover Alcator density scaling, as originally found in analytic work by Molvig and Hirshman. We also find that the universal mode should be stable in ohmically heated tokamaks above a critical beta on the order of 0.02
Magneto-Hydrodynamic Activity and Energetic Particles - Application to Beta Alfvén Eigenmodes.
Nguyen, Christine
2009-01-01
The goal of magnetic fusion research is to extract the power released by fusion reactions and carried by the product of these reactions, liberated at energies of the order of a few MeV. The feasibility of fusion energy production relies on our ability to confine these energetic particles, while keeping the thermonuclear plasma in safe operating conditions. For that purpose, it is necessary to understand and find ways to control the interaction between energetic particles and the thermonuclear...
Alfv\\'en waves in simulations of solar photospheric vortices
Shelyag, S; Reid, A; Mathioudakis, M
2013-01-01
Using advanced numerical magneto-hydrodynamic simulations of the magnetised solar photosphere, including non-grey radiative transport and a non-ideal equation of state, we analyse plasma motions in photospheric magnetic vortices. We demonstrate that apparent vortex-like motions in photospheric magnetic field concentrations do not exhibit "tornado"-like behaviour or a "bath-tub" effect. While at each time instance the velocity field lines in the upper layers of the solar photosphere show swirls, the test particles moving with the time-dependent velocity field do not demonstrate such structures. Instead, they move in a wave-like fashion with rapidly changing and oscillating velocity field, determined mainly by magnetic tension in the magnetised intergranular downflows. Using time-distance diagrams, we identify horizontal motions in the magnetic flux tubes as torsional Alfv\\'en perturbations propagating along the nearly vertical magnetic field lines with local Alfv\\'en speed.
Kuridze, D
2007-01-01
Nonlinear coupling between 3-minute oscillations and Alfven waves in the solar lower atmosphere is studied. 3-minute oscillations are considered as acoustic waves trapped in a chromospheric cavity and oscillating along transversally inhomogeneous vertical magnetic field. It is shown that under the action of the oscillations the temporal dynamics of Alfven waves is governed by Mathieu equation. Consequently, the harmonics of Alfven waves with twice period and wavelength of 3-minute oscillations grow exponentially in time near the layer where the sound and Alfven speeds equal. Thus the 3-minute oscillations are resonantly absorbed by pure Alfven waves near this resonant layer. The resonant Alfven waves may penetrate into the solar corona taking energy from the chromosphere. Therefore the layer c_s=v_A may play a role of energy channel for otherwise trapped acoustic oscillations.
Looking for Cosmological Alfven Waves in WMAP Data
Chen, Gang; Mukherjee, Pia; Kahniashvili, Tina; Ratra, Bharat; Wang, Yun
2004-01-01
A primordial cosmological magnetic field induces and supports vorticity or Alfven waves, which in turn generate cosmic microwave background (CMB) anisotropies. A homogeneous primordial magnetic field with fixed direction induces correlations between the $a_{l-1,m}$ and $a_{l+1,m}$ multipole coefficients of the CMB temperature anisotropy field. We discuss the constraints that can be placed on the strength of such a primordial magnetic field using CMB anisotropy data from the WMAP experiment. W...
Attractors of magnetohydrodynamic flows in an Alfvenic state
Energy Technology Data Exchange (ETDEWEB)
Nunez, Manuel; Sanz, Javier [Departamento de Analisis Matematico, Universidad de Valladolid, Valladolid (Spain)
1999-08-13
We present a simplified form of the magnetohydrodynamic system which describes the evolution of a plasma where the small-scale velocity and magnetic field are aligned in the form of Alfven waves, such as happens in several turbulent situations. Bounds on the dimension of the global attractor are found, and are shown to be an improvement of the standard ones for the full magnetohydrodynamic equations. (author)
Experimental observation of the shear Alfven resonance in a tokamak
International Nuclear Information System (INIS)
Experiments in Tokapole II have demonstrated the shear Alfven resonance in a tokamak by direct probe measurement of the wave magnetic field within the plasma. The resonance is driven by external antennas and is identified as radially localized enhancements of the poloidal wave magnetic field. The radial location agrees with calculations which include toroidicity and noncircularity of the plasma cross-section. Other properties such as polarization, radial width, risetime, and wave enhancement also agree with MHD theory
The Alf'ven Effect and Conformal Field Theory
Tabar, M. R. Rahimi; Rouhani, S
1995-01-01
Noting that two-dimensional magnetohydrodynamics can be modeled by conformal field theory, we argue that when the Alf'ven effect is also taken into account one is naturally lead to consider conformal field theories, which have logarithmic terms in their correlation functions. We discuss the implications of such logarithmic terms in the context of magnetohydrodynamics, and derive a relationship between conformal dimensions of the velocity stream function, the magnetic flux function and the Rey...